Avionics Wiring Harness: A Tutorial

[Eric Page]

In the posts that follow, I’ll show the fabrication and assembly of a short interconnect harness for the Dynon SkyView network. Most other avionics systems will use similar harnesses that can be fabricated in the same way. Hopefully this will help to demystify the wiring of a modern glass panel.

I’ll cover the topic in four parts:


In Part 1, I’ll go through the tools required for the job, and I’ll provide links for examples that I’ve found to work well.
In Part 2, I’ll list the parts and materials required to build a reliable harness, again with links.
In Part 3, I'll show the wiring and connector pinout diagrams.
Finally, in Part 4 I'll demonstrate the process to fabricate a harness from start to finish.

Just because all of this made sense to me when I wrote it, doesn’t mean it will make sense to anyone else, so feel free to ask for an English translation!

[Eric Page]

I would consider the following to be the minimum required tools to fabricate a high quality, reliable harness. Like any other part of your airplane build, using good quality tools will pay dividends in reduced frustration and increased quality of workmanship.

1. WIRE CUTTER

Any decent quality wire cutter will be fine, as long as it makes a clean, square cut and doesn’t crush the wire. Small electronics flush cutters like the Hakko CHP-170 (Hakko (https://hakkousa.com/chp-170-micro-cutter.html) / Amazon (https://smile.amazon.com/dp/B00FZPDG1K/)) are ideal. These are also handy for cleanly clipping cable ties and lacing cord in tight places.

28412

2. WIRE STRIPPER

The key here is to use a stripper that cleanly cuts the insulation from the wire but doesn’t nick any of the wire strands. The wire typically used in aircraft (see Part 2: Materials) has insulation that can be difficult to strip cleanly with a poor stripping tool. My recommendation is the Ideal Industries Stripmaster.

28413

Look for model 45-092 (10-22AWG) or 45-093 (14-22AWG). Replacement blade sets are available to strip wire sizes from 8 to 30AWG in various combinations, and the blades are quick and easy to swap. Used tools are often available on eBay (https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=ideal+stripmaster&_sacat=0) at good prices, perhaps needing a blade set to work like new for the wire sizes you want.



Tool P/N
Blade Set P/N
AWG Crimped


45-090
L-4419
8, 10, 12


45-091
L-4420
10, 12, 14, 16, 18


45-092
L-4421
10, 12, 14, 16, 18, 20, 22


45-093
L-4422
14, 16, 18, 20, 22


45-097
L-4994
16, 18, 20, 22


45-098
L-5361
20, 22, 24, 26, 28, 30


45-099
L-8763
8, 10, 16, 18


3. D-SUB CRIMPER

You can spend many hundreds of dollars on tooling to crimp d-sub pins and sockets, but it’s definitely not necessary. Note that we’re going to be using turned contacts, not stamped-and-formed (I’ll explain why in Part 2). This means you want the 4-way indent type of crimper with a rounded head, not the type with replaceable dies in jaws that hinge open. I use a clone of the Greenlee or Paladin PA1460 that I got on Amazon for $27 (https://smile.amazon.com/dp/B01N3KVX8D/), and it works perfectly.

28414

4. D-SUB PIN EXTRACTOR

Inserting a pin or socket in the wrong connector cavity isn’t matter of if, it’s a matter of when and how often. This is one place where the cheap tool will drive you into a purple-faced rage. Avoid, at all costs, buying the tiny red and white plastic tool (https://www.digikey.com/en/products/detail/cinch-connectivity-solutions-aim-cambridge/40-9865/3830306) with the metal probes at each end. The metal in those things is thin and flimsy so it will break after a few uses, and it’s very easy to stab your hand with the other end while using it.


28415
Avoid this tool!

Instead, I would strongly recommend buying the Harting Electronics 09990000368 D-Sub Removal & Insertion Tool (Digi-Key (https://www.digikey.com/short/3zq0m2qt) / Mouser (https://www.mouser.com/ProductDetail/HARTING/09990000368?qs=%2Fha2pyFadugVq%252By%252B5D8b2yUKn B%252B1nbmIlsaXulySLL7ImcshPjnYow%3D%3D) / eBay (https://www.ebay.com/itm/294222309022)). The business end of this tool is made of stouter material, it has a handle big enough for human hands, and the retractable probe cover will protect the tool between uses. Even at $30, this little tool is a bargain. It can still be bent, so don’t go full gorilla on it.

28416
This is the tool you want.

5. HEAT GUN

Any model will do, and you’ll finally get to use that strange curved attachment that came with it.

6. LABEL PRINTER

You can get a decent electronic label printer at any office supply store or online for not much money, so there’s no reason not to clearly label your wires and harnesses. If you use printable heat shrink tubing, you can label individual wires directly, and you can use standard label tape to mark harness connector backshells. Virtually all of the label printers on the market have refill cartridges available with either label tape or heat shrink.

[Eric Page]

1. WIRE

The usual choice for aircraft wiring is MIL-W-22759/16 (often abbreviated as M22759/16). It’s a multi-strand tinned copper wire coated with Ethylene Tetrafluoroethylene (Tefzel) insulation. The basic part number is followed by two “dash numbers.” The first indicates wire gauge and the second, insulation color.

28417

There are a few additional color codes that are fairly uncommon in the wild: P = pink, T = tan, D = dark (i.e. D6 = dark blue), L = light (i.e. L6 = light blue). Striping is indicated by two color numbers: -90 would be white with black stripe. Twisted pairs are sometimes called out by separating the conductor colors with a forward slash: -95/96 would be a twisted pair composed of white with green stripe and white with blue stripe.

It’s perfectly acceptable to use one color – usually white – for everything, but if you do this be sure to do a good job labeling your wires, twisting the correct pairs and keeping the pinout matched from end to end in harnesses.

If buying wire in 100’ increments in standard colors, Skygeek has good prices (https://skygeek.com/shop/?search_query=M22759%2F16).

For shorter lengths, or for custom color striping, ProWire USA is a great source (https://prowireusa.com/c-32-m22759-16.html). They have a 10’ minimum for standard colors and they make custom striped wire at very reasonable prices with a 100’ minimum.

Also be sure to check the Bargain Bin at American Wire & Cable (https://www.awcwire.com/discount-wire-and-cable?bargainBinCategory=wire) (click “MIL-Spec Wire & Cable” in the menu on the left, then “M22759”).

2. D-SUB CONNECTOR BODIES

This is one item for which Aircraft Spruce is very competitive on price. They sell good quality AMP connector bodies cheaper than any place I’ve found. Common sizes hold 9, 15, 25, 37 or 50 pins. Your avionics installation manuals will describe the sizes you need. Pay attention to connector gender, which is determined by contact type, not connector body. The female connector uses sockets and the male uses pins, but the female connector fits inside the male.

28418
Top: male. Bottom: female.

Links to connector bodies at Aircraft Spruce:


9-Pin
Male (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-12150.php)
Female (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-12149.php)


15-Pin
Male (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-11892.php)
Female (https://www.aircraftspruce.com/catalog/elpages/15pinfemcrimpd.php)


25-Pin
Male (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-11893.php)
Female (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-12153.php)


37-Pin
Male (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-12152.php)
Female (https://www.aircraftspruce.com/catalog/elpages/pinconnector11-12151.php)


SteinAir stocks similar connectors (https://www.steinair.com/product-category/connectors/d-sub/?product_count=40), including 50-pin and high density types, as well as contacts, backshells and cinch nuts.

Be careful not to buy high density connectors or contacts unless that’s really what you need.

3. D-SUB CONTACTS (PINS & SOCKETS)

As I mentioned in Part 1, I recommend using turned, not stamped-and-formed contacts. The turned parts are more expensive, but they’re much easier to use, and to get consistently good results with. A cheap, generic 4-way indent tool will crimp turned pins and sockets just fine. Finding a tool with good dies for stamped-and-formed contacts is a challenge at reasonable prices, and getting consistently good results with them takes skill and practice.

Turned pins for male connectors – P/N: M39029/64-369 or 205089-1
Turned sockets for female connectors – P/N: M39029/63-368 or 205090-1

Both are available from any electronics parts distributor, or from...

B&C Specialty Products (pins (https://bandc.com/product/d-sub-pin-standard/) / sockets (https://bandc.com/product/d-sub-socket-standard/))
SteinAir (pins (https://www.steinair.com/product/contact-standard-dsub-pin/) / sockets (https://www.steinair.com/product/contact-standard-dsub-socket/))
Aircraft Spruce (pins (https://www.aircraftspruce.com/pages/el/cablecableaccessories_dconnectors/malepin11-00139.php) / sockets (https://www.aircraftspruce.com/pages/el/cablecableaccessories_dconnectors/femdpincrimp.php))

There’s also an eBay seller offering bags of 100 at very attractive prices (pins (https://www.ebay.com/itm/254848270431) / sockets (https://www.ebay.com/itm/265196240319)).

4. D-SUB BACKSHELLS

This is the plastic or metal case that holds the connector body and provides strain relief for the wires. You can spend a small fortune on fancy metal backshells, but I wouldn’t bother. The Dynon factory uses inexpensive plastic parts (Assmann WSW “A-FT” series (https://www.digikey.com/short/f80b8v87)). You’ll need one for each d-sub connector you install.

SteinAir sells similar parts (https://www.steinair.com/page/1/?s=dsub+backshell&post_type=product&dgwt_wcas=1&product_count=16) at similarly low cost.

5. D-SUB CINCH NUTS

The Assmann WSW “A-FT” series backshells come with thumbscrews to hold the (usually female) connector in place. Those work great in cases where your harness will connect to an avionics box that has a (usually male) connector with cinch nuts already installed. However, if you need to make an extension harness with both male and female ends, you’ll need a pair of cinch nuts for the male end (in place of the thumbscrews), so that a female connector’s thumbscrews can clamp the connectors together.

You’ll need so few of these that there’s little point in shopping around. Aircraft Spruce sells them in a complete set (https://www.aircraftspruce.com/catalog/elpages/femalescrew11-11896.php), with washers and #4-40 hex nuts to install them on the connector body, for $1.35/set. If you prefer, SteinAir sells connector bodies with cinch nuts already installed (https://www.steinair.com/?s=d-sub+%234-40&post_type=product&dgwt_wcas=1).

Note that you may have to clip away part of the molded internals of the backshell to install a connector with cinch nuts attached.

6. HEATSHRINK TUBING

The good stuff is so cheap, there’s no reason to use anything else. I use Qualtek "Q5-3X" series, which has a 3:1 shrink ratio (meaning it shrinks to 1/3 of its original diameter) and is both adhesive-lined and flame retardant. Digi-Key carries it in several useful diameters (https://www.digikey.com/short/frftvnjc), in 4’ lengths.

I find that the 0.354” inside diameter Q5-3X tubing is a good fit over expandable sleeve on a 9-wire Dynon SkyView network harness.

7. EXPANDABLE SLEEVING (OPTIONAL)

This stuff isn’t strictly necessary, but it makes for a professional looking harness. If you prefer not to use expandable sleeve, then wire bundles can be dressed with nylon cable ties or lacing cord. For expandable sleeve, I use Techflex Clean Cut FR (https://cdn.techflex.com/assets/pdfs/catalog/ccf.pdf). 1/4” diameter sleeve costs ~$0.53/ft in 100’ rolls (https://www.digikey.com/en/products/detail/techflex/CCF0.25TB100/2502501). It will easily expand (like a Chinese finger puzzle) to cover wire bundles up to about double its nominal diameter, so I don’t bother with the larger, more expensive sizes. The main advantages in using expandable sleeve are that the harness remains more flexible than if it’s dressed with cable ties or lacing cord, and it’s less likely to get caught on something while it’s being fished through the aircraft.

[Eric Page]

Below are the example diagrams and tables that I’ll use to build a harness in Part 4. They show the pinout, wire colors and twist callout for a Dynon SkyView network cable.

NOTE: There is an error in the connector diagram. Dynon’s avionics have male connectors for SkyView network connections, so harnesses need female connectors. In the diagram below, Dynon refers to the connector as a D9M (male), when it should be D9F (female). The contact locations shown are correct for a female connector.

28419

Pay careful attention to the note below the connector diagram, which indicates that it’s a view looking at the contact insertion side of the connector, not the mating side. These location numbers are molded into the plastic lining of the connector body on both sides, but magnification is needed to see them.

28420

I’ll be using wires matching the Dynon color scheme in Part 4, but as I said in Part 2, using all one color is fine as long as you’re careful to match pin numbers at each end and twist the correct wire pairs.

Speaking of twist, here are the tables showing which wires do what in the SkyView network, and how to twist them within a harness.

28421
28422

Finally, I’ll offer another reminder about pin mirroring between male and female connectors. In order for the connectors to mate with the correct wires connected, the male and female parts have their contacts in mirrored locations. It’s very easy to forget which type you’re fabricating, so pay careful attention and consider keeping separate diagrams in front of you depending on which type you’re working with at the moment.

28423
Male D-Sub Pinout (Crimped Pins)
Contact Insertion Side View

28424
Female D-Sub Pinout (Crimped Sockets)
Contact Insertion Side View

[Eric Page]

1. ADJUST CRIMPING TOOL

First, we need to adjust the crimping tool so that contacts sit at the correct depth and are crimped in the right place. Insert a pin or socket, with its striped wire cavity facing out, into the little hole in the flat face of the tool. On the opposite side of the tool, turn the knurled collar to adjust the contact stop until the end of the pin/socket is flush with the flat face of the tool. If you wish, you can apply a dab of super glue to keep the collar from moving.

28425 28426

2. DETERMINE HARNESS LENGTH

You can do this with a piece of wire or string, or for very short cables, a calibrated eyeball. Be sure that your test wire/string follows the same path your harness will follow, and accounts for cable ties or lacing cord securing it to the aircraft structure.

Consider adding a few inches to allow for the vagaries of routing, then add a bit more to allow for shrinkage when the wires are twisted. You’ll be much happier if a harness is a bit longer than necessary than if it’s 3” too short!

3. CUT WIRES

Pull your wires off the spools and cut them to length. In a Dynon SkyView network harness, the orange wire (contact #5) isn’t twisted, so it doesn’t need that extra length. It can be cut to match the other wires after they’re twisted, then be prepared in the same way and added to the first connector before completing step 8.

In this example I’m making a very short cable to daisy-chain components that are close to one another, so my wires will only be about a foot long.

28427

4. PREPARE WIRE ENDS

At one end of each wire, strip about 0.16” of insulation (you’ll get an eye for this after doing it a few times). Test your strip length by inserting the wire into the cavity of a pin or socket. It should bottom out before the insulation touches the contact, and the wire strands should be visible in the tiny witness hole.

28446

5. CRIMP CONTACTS

Using your crimping tool, crimp a pin/socket on the prepared end of each wire. Insert the contact into the tool, then insert the wire into the contact’s wire cavity. While holding the wire and contact in place with one hand, fully cycle the tool with the other.

28428

6. POPULATE CONNECTOR

Insert each crimped contact into the connector body in the location corresponding to its wire color in the diagram. Push the contact in until you feel or hear it click. An insertion and removal tool can be used for this if you wish, but pushing on the wire is usually sufficient to seat the contact. While inserting, try not to sharply bend the wire where it exits the contact. Once seated, give each wire a tug to be sure it’s secure.

If you make a mistake and put a wire in the wrong location, use the insertion and removal tool to take it out. Lay the wire into the metal channel of the tool, then push-and-wiggle the channel into the contact cavity in the connector body. You’ll feel the tool bottom out against the contact, then push-and-wiggle some more and it will move a bit further, unlatching the contact. Pull on the wire to withdraw the contact and tool together.

28430 28431

7. TWIST WIRE PAIRS

A. First, make a simple twist gauge. Cut a piece of cardboard to 4” in length and make five marks on it, 1” apart. By comparing these marks to the twisted pair, and matching one twist per mark, it will indicate when you reach 12 twists per foot. This over-twist to 12 per foot is required due to wire spring-back in order to achieve the 8-10 twists per foot specified by Dynon.

28432

Another technique is to calculate the number of turns required based on length (i.e. 7 ft 6 in harness x 12 twists per foot = 90 twists). Put a tape marker on the drill chuck in step C, below, and count rotations until you reach the required number.

B. Without distorting its metal shell, hold the connector body in a bench vise with the wires trailing out to one side. Separate one pair of wires to be twisted and pull them out horizontally from the connector.

28433

C. Insert the loose ends of the wires into a drill chuck and tighten the chuck to hold the wires firmly. At low speed, run the drill motor to twist the wires.

28435

D. Hold the drill in one hand and the cardboard twist gauge in the other. Once you reach 12 twists per inch, hold the wires firmly while you release them from the drill chuck; if a long twisted pair gets away from you, you’ll have a rat’s nest to unwind. Slowly release your grip on the wires, allowing them to untwist a bit without pulling toward the connector, until they’re relaxed.

28436

Repeat this process for each of the other pairs that need to be twisted.

28437

8. DRESS HARNESS

NOTE: Add the orange wire at this point if you’re making a Dynon SkyView network cable.

If you’re using cable ties or lacing cord, apply them periodically along the length of the harness to contain the wires.

If you’re using expandable sleeve, cut a piece long enough to fit between the connectors, with about 1/2–3/4” of gap between the end of the sleeve and the connector body at each end.

28438

Slide the sleeve over the wires to contain the harness, then slide two ~2” long pieces of heat shrink tubing over the sleeve. At the end with the connector attached, use your heat gun to shrink one piece of heat shrink tubing over the wires and the loose end of the sleeve.

28440 28441
28439

9. INSTALL BACKSHELL

Put the small cable grip saddle into the backshell cavity opposite the screw holes. Lay the populated connector body into the backshell with the connector’s metal edge just behind the lip of the backshell and the heat shrink tubing laying over the cable grip saddle. Put the thumbscrews into the backshell with their retaining ridge between the molded retainers in the backshell and their threaded ends poking through the ears of the connector body.

28442 28443

While keeping the thumbscrews and cable grip saddle in place, close the backshell’s lid and squeeze until it clips closed. Using the two small screws, tighten the cable grip saddle to retain the heat shrink and prevent any strain on the wires or crimped contacts.

28444

10. TERMINATE OPPOSITE END

If the wires at the unfinished end are slightly uneven in length, trim them to match the shortest wire, then install the contacts, connector body, expandable sleeve, heat shrink tubing and backshell by repeating steps 4, 5, 6 and 9. Be careful to maintain twist on the twisted pairs, and to match the wire locations end-to-end. Don’t worry if the expandable sleeve unravels a bit while you’re working; it will be captured under the heat shrink tubing, never to be seen again.

11. LABEL HARNESS

Using your label printer, make labels and apply them to the connector backshells to identify function.

28445

Congratulations – you now have a well made, professional looking harness!

[airlina]

Eric , fantastic tutorial - I know this had to take some of your precious build time to prepare and photograph and post, but guys preparing for this part of their builds will really appreciate your time and effort. Generous members like you make this a great forum . Thanks for sharing Bruce N199CL

[bumsteer]

Excellent tutorial Eric!! Thank you for taking the time and sharing your expertise.

Rick

[alexM]

Wow, awesome tutorial.

Can you explain when/why twisting is needed? My understanding is quite murky on that one. Say for example the wires going to the wing tip strobes. Do yo twist those? Do you keep twisted wires away from non twisted wires (say, magnetometer)?

[jrevens]

That had to take a lot of time, Eric. It should be really helpful for many builders… great job!

[Eric Page]

Thanks, everyone; I'm glad it's well received. On the 'net you never know when someone will shoot you full of holes!


Can you explain when/why twisting is needed? My understanding is quite murky on that one. Say for example the wires going to the wing tip strobes. Do yo twist those? Do you keep non twisted wires away from non twisted wires (say, magnetometer)?
Keep in mind that I'm not an electrical engineer (or any other kind, for that matter). I'm a bit murky as well, but here goes...

As I understand it, twisting helps to mitigate the effects of electromagnetic interference. It places the two wires the same average distance from any source of interference, which means the noise induced in the pair will be the same on both wires (called "common mode"). That's easier for a receiving circuit to filter out because it's looking for a difference between the pair, and any noise that's common to both isn't a difference, so it isn't detected.

Apparently it also reduces the pair's ability to transmit interference as well, but I can't begin to explain that.

Computer network cables specify different twist rates (twists per meter) for each pair in the cable, so that the same wires in each pair don't lie next to each other on every twist (eliminates "crosstalk"). This begs the question why Dynon doesn't specify different twist rates for the pairs in their cables. Perhaps the two communication pairs are redundant/duplicates carrying the same data, so interference between them isn't a concern? I suspect there's a fairly steady current draw to a SkyView system over short time scales, so twisting the two pairs of power wires is a belt-and-suspenders kind of thing that could probably be eliminated at no cost to function.

Anyway, I would say to just follow each manufacturer's recommendation on wiring their particular appliance. I did try to keep all other wires in my wings away from the magnetometer cable. All of my lighting wires (landing/taxi and wingtip NPS) are just 2 and 4-conductor unshielded cables. I did pass them all through the rear spar, which should provide some shielding effect, while the magnetometer cable is outside the spar.

Honestly, if it weren't made of solid core 26AWG wire and PVC insulation, I'd probably just use the spool of Cat6 Ethernet cable left over from wiring my house for all the SkyView network cables in my plane, and save myself all this twisting shenanigans.

The best things you can do to prevent problems for yourself are to be sure your antenna cables are well made, with high quality connectors that are properly installed (so there's no RF leakage that might effect other electronics), and be careful to closely follow MGL's guidance on shielding and grounding when wiring audio circuits. Isolate headphone and microphone jacks from metal structure, be sure that shielded audio cables have their shields grounded at only one end (usually at the intercom/radio where they start), and tie audio grounds/shields solidly to the place specified in the installation manual.

[mike92104]

I'd like to add that Aircraft Tool Supply has many of the electrical tools you may need (and many others) for very reasonable prices.

https://aircraft-tool.com/shop/search.aspx?CATEGORY=Electrical

[alexM]

3. D-SUB CRIMPER

You can spend many hundreds of dollars on tooling to crimp d-sub pins and sockets, but it’s definitely not necessary. Note that we’re going to be using turned contacts, not stamped-and-formed (I’ll explain why in Part 2). This means you want the 4-way indent type of crimper with a rounded head, not the type with replaceable dies in jaws that hinge open. I use a clone of the Greenlee or Paladin PA1460 that I got on Amazon for $27 (https://smile.amazon.com/dp/B01N3KVX8D/), and it works perfectly.

This is super useful information. I currently have a Daniels AFM8 on my ebay watch list. I used one previously when I installed the COM and TXP equipment in my Citabria and the T-6 (under supervision of course). It is also mentioned in the aircraft electrical book I bought, so I thought it was required equipment. That Daniels AFM8 is $250-ish used, and it doesn't come with the "positioner" which is an easy $55-80 each. With the Daniels tool you don't adjust anything, it just works flawlessly.

Now with your recommendation I would say that for 1/10 the cost I can fiddle around adjusting for a moment or two.

[DesertFox4]

I purchased several wiring tools from SteinAir one of our site sponsors up in Minnesota. Check out their website but they have lots more than is on their site also especially avionics.

[jiott]

I got all my wiring tools from SteinAir; very happy with them.
The wire stripper was the most expensive, but is also the most used and lots of time saved.

[napierm]

Thanks, everyone; I'm glad it's well received. On the 'net you never know when someone will shoot you full of holes!


Keep in mind that I'm not an electrical engineer (or any other kind, for that matter). I'm a bit murky as well, but here goes...

As I understand it, twisting helps to mitigate the effects of electromagnetic interference. It places the two wires the same average distance from any source of interference, which means the noise induced in the pair will be the same on both wires (called "common mode"). That's easier for a receiving circuit to filter out because it's looking for a difference between the pair, and any noise that's common to both isn't a difference, so it isn't detected.

Apparently it also reduces the pair's ability to transmit interference as well, but I can't begin to explain that.


I am an EE so I'll give it a go. The reason to twist the wire with its ground is to average out the induced voltage. Any stray AC magnetic field will induce a voltage in a loop of wire. Make the wires very close together and minimize the size of the loop. Twist the wires and they spend 1/4 the time facing the field and 1/4 away. Averages out to 0. And 1/2 the time they are at right angles to the field so the induced voltage is also 0. Note this is most effective for low frequency. At high frequency (RF, ignition impulse noise) the field can couple onto the wire pair like an antenna. The solution is a shield that is terminated only at one end: at the power ground of the instrument. Thus the shielded twisted pair.

Similar situation with transmitted EMI. The generated magnetic field follows the wire (right hand rule) and gets bigger with the size of the loop. Minimize the loop size. Twist the wires and the magnetic field goes + and -. Averages out to 0.

Hope this helps.

[napierm]

The problem I have with these crimpers is that there isn't a calibrated adjustment for the depth of crimp. If they are adjustable at all then you could use set of pin gauges (go/no go) to set them. The crimp depth is set for the size of terminal as well as the wire gauge.


"3. D-SUB CRIMPER

You can spend many hundreds of dollars on tooling to crimp d-sub pins and sockets, but it’s definitely not necessary. Note that we’re going to be using turned contacts, not stamped-and-formed (I’ll explain why in Part 2). This means you want the 4-way indent type of crimper with a rounded head, not the type with replaceable dies in jaws that hinge open. I use a clone of the Greenlee or Paladin PA1460 that I got on Amazon for $27 (https://smile.amazon.com/dp/B01N3KVX8D/), and it works perfectly."


This is super useful information. I currently have a Daniels AFM8 on my ebay watch list. I used one previously when I installed the COM and TXP equipment in my Citabria and the T-6 (under supervision of course). It is also mentioned in the aircraft electrical book I bought, so I thought it was required equipment. That Daniels AFM8 is $250-ish used, and it doesn't come with the "positioner" which is an easy $55-80 each. With the Daniels tool you don't adjust anything, it just works flawlessly.

Now with your recommendation I would say that for 1/10 the cost I can fiddle around adjusting for a moment or two.

[efwd]

That has clarified many questions I have had and resolved to just never ask. Thanks for posting that Napierm.

[Eric Page]

The problem I have with these crimpers is that there isn't a calibrated adjustment for the depth of crimp. If they are adjustable at all then you could use set of pin gauges (go/no go) to set them. The crimp depth is set for the size of terminal as well as the wire gauge.
Well, I'm not sure what to say about that except that I've pull tested the crimps that mine makes on standard density d-sub contacts with 22AWG wire and found them to be plenty strong enough. How strong? I didn't put a scale on it, but given that the backshell provides strain relief I'm not at all worried about wires pulling loose from their contacts.

B&C sell the Paladin PA1460 ($49) and SteinAir sell a crimper ($38) identical the one that I use. I'll bet a lot of E-AB aircraft have been successfully wired with them.

I wish I had the budget to buy NASA-spec tooling for every task, but sadly I'm just not that builder. I sure envy the guys who do.

[tdldedcd]

Eric, great post. Thanks for taking the time to put together such a complete and in-depth description for wiring. I'm not quite there yet, but will be referring to your post regularly once I start.

[efwd]

I agree with John. I didn't care for the wire showing at the base of the pin on the video. These pics are helpful in that the wire is pushed in all the way as well as the mention of setting the depth. I was not aware of that function, had to figure that out for myself back then. Thanks Eric.

[alexM]

I just want to bump this thread because it is so useful. I just ordered all the tools and a boat load of wire using the links Eric provided.

I'm also here to ask a follow on question. When I bought my brand M avionics I got their wiring harnesses. All (most anyway) of my sub D connectors are already done. In come cases there is enough wire that I can connect the various contraptions together directly but in others I will need to butt splice wires and put heat shrink over the top of them. I did plenty of that in my previous installations so I'm comfortable with the work.

After placing my orders I realized that I didn't see butt connectors mentioned. A google search produced the following hit:
wow that's a long link (https://www.delcity.net/store/Non-Insulated-Butt-Connectors/p_801870.h_801879.r_IF1003?identifiers=pla-4577885387334979&Campaign=Shopping+-+Catchall&CampaignId=445029913&AdGroup=Catchall&AdGroupId=1188573056390575&AdId=74286034062410&Network=s&msclkid=8b3f89a6962e19a20ac0edb9b267e340)
Are these up to the task or do I need to go somewhere else? They look identical to the ones I used but I don't know crap when it comes to this stuff.

I also just realized that I'll have a bunch of terminals to crimp and I didn't see that tool on the list. The one I borrowed when I was doing supervised work was a fancy ratcheting tool that wouldn't let go until you had crimped the terminal sufficiently. I'd like something like that if you have any suggestions.

[MikeFairbanks]

I spent 12 years in the military as an avionics tech... went through aviation soldering and connector repair school, and for the last 25 years have worked in the satellite communications industry, where I had to get my NASA soldering certification.

First I want to respond to the comments that didn't like the exposed wire on the crimped pins. When I went to school for this if you brought up work that had the insulation right up against the pin you failed. I was taught that there should be a slight gap there... if you can push the insulation all the way up against the pin or cup, then you can't really be certain that the wire completely fills the pin or cup.

Second, regarding butt splices. I like the hermetic sealing splices with the solder ring in them. What you have to be careful of with these though is that there is not enough solder in that ring for bare wires... you need to tin your wires before using them. The ring is just to bond the tinned wires together. If you use them with bare wires it will probably stick them together, but the electrical connection will be questionable, and occasionally you'll be able to pull them apart. We used these on F/A-18's in the military, so if you use them right there is nothing wrong with them.

http://tinyurl.com/23uuv8s6 here's an example

[bumsteer]

Hi Alex

I purchased the ratcheting crimper I'm using from Aircraft Tool Supply. The crimper itself is P/N E300-002. It was in a kit with a bunch of terminals that I purchased at Oshkosh. It came with jaws for crimping ring/spade etc. terminals.You can then purchase jaws for BNC and open barrel connectors. You can probably find it elsewhere also. Works great.

Rick

[jiott]

I got my crimpers, wire stripper, etc. from SteinAir.

[Eric Page]

The problem with @alexM's linked butt splices is that they provide no insulation support, so the wires are permitted to bend where they exit the crimp. Since the goal of a crimped connection is to crush the wire and connector into a homogenous, gas-tight mass, you essentially turn a stranded wire into a solid one. If that solid conductor is allowed to bend, it may crack and break. Hence the need for insulation support -- to prevent the wire from bending at the crimp.

There are a few ways to skin this cat:

1. The gold standard: Use TE Connectivity AMP PIDG butt splice terminals, which include a metal insulation support crimp. Note that there are numerous kinds of insulated butt splices out there. The ones with brightly colored opaque insulation (available at hardware and auto parts stores; like this (https://www.amazon.com/dp/B0BMZYLY37/)) are not suitable for aircraft use, as their insulation crimp is accomplished only by the plastic covering. With age and heat cycles, the plastic will suffer from... well... plastic deformation: they'll eventually let go of the wire insulation. The PIDG's metal insulation support crimp won't let go. You can get PIDG butt splices from B&C Specialty Products (https://bandc.com/product/butt-splice-terminal/), SteinAir (https://www.steinair.com/?s=butt+splice+terminal&post_type=product&dgwt_wcas=1) or any decent electronic component supplier. Both B&C (https://bandc.com/product/pidg-style-crimp-tool/) and SteinAir (frame (https://www.steinair.com/product/ratcheting-crimper-frame-only/) | die (https://www.steinair.com/product/insulated-terminal-die-only/)) sell crimp tooling at reasonable prices (which will also crimp PIDG ring and Fast-On terminals). This is the quickest and easiest solution: strip wires, make two crimps, done.

2. The butt crimps that @alexM linked above can be used, along with two layers of adhesive-lined heat shrink. Cut one piece (smaller diameter) about an inch longer than the gap between insulation ends on the wires, and the second piece (larger diameter) about an inch longer than that. Center the first piece over the crimp, shrink it, then center the second piece over the first and repeat. You're using two layers because hot glue doesn't make a chemical bond and tends to let go when it's flexed, especially when it's cold.

3. Use adhesive-lined solder sleeves. I have no personal experience with these but they seem to work, and one of the big names in connectors and heat shrink products (TE Connectivity Raychem) make some of them. As you'll see in this Kitplanes article (https://www.kitplanes.com/solder-sleeves/) comparing different brands, the installation process can be difficult to get right. SteinAir (https://www.steinair.com/?s=solder+sleeve) sells the RayChem version in three different sizes, as well as sleeves with a pigtail lead-out wire and a torch for installation. That link also has a video from Stein showing how to install them. The other brands tested by Kitplanes are all over Amazon (https://www.amazon.com/s?k=solder+sleeve) and eBay (https://www.ebay.com/sch/i.html?_nkw=solder+sleeve).

[Eric Page]

What you have to be careful of with these though is that there is not enough solder in that ring for bare wires... you need to tin your wires before using them. The ring is just to bond the tinned wires together. If you use them with bare wires it will probably stick them together, but the electrical connection will be questionable, and occasionally you'll be able to pull them apart. We used these on F/A-18's in the military, so if you use them right there is nothing wrong with them.

Be very careful here. The amount of solder in these sleeves is engineered to provide an electrical and mechanical connection without providing enough solder to wick up the wire and stiffen it beyond the glue ring. If you tin the wires before inserting then into the splice, there's a very good chance that you'll wick enough solder up the wire (inside the insulation) to defeat the purpose of the insulation support. This can result in a wire that breaks inside its insulation, making a difficult-to-troubleshoot intermittent fault.

[Eric Page]

Here's a tutorial by Bob Nuckoll's showing how to do another wire splicing technique, the soldered lap splice (http://www.aeroelectric.com/articles/Solder_Lap_Splicing/Solder_Lap_Splices.html). This obviously carries similar risk to tinning wires before using solder sleeves, so good technique and minimum solder is called for.

This tutorial (http://www.aeroelectric.com/articles/multiplewires/multiplewires.html) shows how to terminate multiple wires into a single PIDG terminal or splice.

[Eric Page]

All (most anyway) of my sub D connectors are already done. In come cases there is enough wire that I can connect the various contraptions together directly but in others I will need to butt splice wires and put heat shrink over the top of them.
Another technique to consider, if you just need to extend MGL-supplied wires that are pre-terminated with D-Sub pins or sockets, is to crimp the mating pins or sockets to the extension wires, mate the terminals and cover with adhesive-lined heat shrink. Offset each connection by an inch or so to keep bundle diameter to a minimum.

Links for D-Sub pins and sockets are at item 3, in post #3, above (https://teamkitfox.com/Forums/threads/11670-Avionics-Wiring-Harness-A-Tutorial?p=100626&viewfull=1#post100626). The links to eBay are dead; here are new ones to search for pins (https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=%28%22M39029%2F64-369%22%2C%22205089-1%22%29&_sacat=0) and sockets (https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=%28%22M39029%2F63-368%22%2C%22205090-1%22%29&_sacat=0).

[Danilo]

Thanks Eric for this post. Gonna be wiring a g3x panel on my build and this is super helpful!

[tdldedcd]

Eric, thanks for all the posts you have done in regards to wiring. It has been extremely helpful to myself and many others. I have another one for you. I have 2 Ray Allen control sticks with trims switches. I need to bring them together with the panel mounted trim switch and then back to the GA28. What is the best way to bring these wires together? Do I need to utilize a mixer?

Thanks again for all your help.

[Eric Page]

I have 2 Ray Allen control sticks with trims switches. I need to bring them together with the panel mounted trim switch and then back to the GA28. What is the best way to bring these wires together? Do I need to utilize a mixer?
I presume you mean GSA28, Garmin's autopilot servo. The GA28 appears to be a marine GPS antenna...

Just to clarify, are we talking about flaperon trim via the GSA28 servo, or elevator trim via the Kitfox-supplied DC linear actuator?

If you mean elevator trim, then how/why is the GSA28 servo involved?

Set me straight on those questions and I'm sure we can get your trim sorted out!

[Eric Page]

OK, after sleeping on this, I've decided that I might be misunderstanding the way Garmin handles trim.

Does the Garmin autopilot accomplish pitch trim using only the elevator servo (i.e. no control of the Kitfox stabilizer actuator)?

Or, does the Garmin pitch servo do two things: 1. control the elevator; and, 2. pass trim commands to the stabilizer actuator from either the instrument panel control head or the trim switches?

I guess I'm just thoroughly confused!

What I really need to know is, where are the signals from your trim switches going, and does the receiver want to see 12V or ground from the switches to command the trim motor to run?

Also, what are the current limits of whatever Garmin device is directly driving the Kitfox actuator?

[tdldedcd]

Hi Eric,

After re-reading my post, I realize it was clear as mud. The flow of the system is trim switch (pilot/co-pilot Ray Allen G4 control sticks) to the GSA28 to the Safety Trim and out to the Kitfox trim actuator.

I've attached the schematic from Safety Trim.

32810

I'm comfortable with the all of this. My confusion is in having multiple trim switches. Both G4 grips will have trim switches. Do the switch wires need diodes in place before they are brought together?I think I might have found the answer in a different Safety Trim product manual.
32811
My switch wiring will go to the GSA28. If I'm reading this right, the wires from each grip trim switch can be combined and then sent to the GSA28 without the use of diodes. Do you see it the same?

Thanks for your time with this.

[Eric Page]

OK, that first TCW diagram (page 4, here (https://www.tcwtech.com/wp-content/uploads/2020/06/725.0025-Install-Instr-1.3-ST-1-1224V-10A-BSTR.pdf)) explains a lot. I was unaware that the GSA28 handled pitch trim through a separate motor, in addition to direct pitch control via its own servo. Strange arrangement, but I guess it works. It's really not that much different from the Dynon system, except that Dynon routes the switch signals through the autopilot module on the instrument panel.

WRT your question, no, you don't need any diodes or mixer in the circuit. Just parallel all of the switches together as shown in the second diagram (TCW App Note #1 (https://www.tcwtech.com/wp-content/uploads/2020/04/Safety-Trim-Application-Note-Multiple-Switch-Wiring-Details.pdf)). There's no practical limit on the number of switches that can be paralleled this way.

[tdldedcd]

Perfect. Thanks Eric!!

[alexM]

WRT your question, no, you don't need any diodes or mixer in the circuit. Just parallel all of the switches together as shown in the second diagram (TCW App Note #1 (https://www.tcwtech.com/wp-content/uploads/2020/04/Safety-Trim-Application-Note-Multiple-Switch-Wiring-Details.pdf)). There's no practical limit on the number of switches that can be paralleled this way.

Okay, type real slow for me here so I can hopefully understand. Why do they show diodes used in this installation where I'll have the two hat switches and the rocker switch on the center console?
32840

[Eric Page]

Why do they show diodes used in this installation where I'll have the two hat switches and the rocker switch on the center console?
That's an excellent question. All the switches are doing is pulling the input on the trim controller (Garmin GSA28, Dynon A/P Panel, TCW Safety-Trim, whatever MGL uses) to ground. There's no current steering or blocking required to do that, and no switch should care what the others are doing.

Unless there's something strange about the way the Ray Allen RS-2 switch works, the diodes shouldn't be necessary. That said, a SPDT switch has three terminals; what's the unconnected white/black wire on the RS-2 for? I guess if you're using the RA switch, install the diodes. Or call TCW or RA and ask if they're really needed.

For a bog-standard SPDT rocker, or ten of them in parallel, no diodes.

Incidentally, the Kitfox-supplied rocker switch that came with the Series 5 (and presumably later models) is DPDT, because it was used to switch and reverse motor power directly. If you use that switch with a modern EFIS setup that controls trim for autopilot functions, it's only necessary to use three of the six switch contacts, all on one side of the switch (i.e. just treat it as a SPDT switch). Center terminal to ground, the other two to "up" and "down".

If one of the switches makes the motor run the wrong direction, swap the "up" and "down" wires on the switch. If all switches make the motor go the wrong direction, swap the wires on the motor.

[Geek]

Okay, type real slow for me here so I can hopefully understand. Why do they show diodes used in this installation where I'll have the two hat switches and the rocker switch on the center console?
32840

OK Alex. Just for you. Sloooooooowwwwww. Eric got it. The diodes are required in this use because of the internal wiring of the Ray Allen RS2 trim switch. Specifically that switch. Here's why right from Ray Allen: (the bold/underline is from me)

"The RS2 rocker switch provided with your RayAllen trim system is designed to electrically short the servo motor to ground (-) when released. This stops the output shaft without any coasting, allowing precise positioning when trimming your aircraft. The RS2 rocker switch is rated at 1 amp.
NOTE: If you want to use this rocker switch along with a stick grip mounted switch, or any other switch, to simultaneously control a servo, you must use a different wiring diagram (available through our web site at www.rayallencompany.com)."

Here's a link to the Ray Allen site that specifically addresses that switch. http://www.rayallencompany.com/RACmedia/instructionsRS2withmods.pdf

The Garmin system has two ways of addressing pitch trim. One is adding a second GSA28 that is trim only (but this doesn't work for Kitfox trim). The other is to identify to the GSA28 that you are using a separate motor to control the trim (like we do with the Kitfox) and wire the commands to the motor through pins 13 and 14. BUT those commands are limited to 1Amp which is why the Safety Trim system is added in series between the GSA and the trim motor; it supplies the current for the trim motor when it gets the trim input from the autopilot through the GSA28.

Hope this helps. I can provide you a schematic of how I did mine for the stick grip trim but I didn't use the console switch. As Eric pointed out - you can put in any number of switches without an issue.

Geek

[Eric Page]

"The RS2 rocker switch provided with your RayAllen trim system is designed to electrically short the servo motor to ground (-) when released.
OK, after reading through the RS-2 document (http://www.rayallencompany.com/RACmedia/instructionsRS2withmods.pdf) that Gary linked to, it makes sense. Thanks, Gary.

What RA have done is to build a DPDT switch by mounting two separate SPDT switches inside a custom enclosure, then wiring them together to make a motor reversing circuit (see Diagram 1; this is just like what Kitfox instructs us to do with their factory-supplied switch). RA have taken care of the confusing crossover links at the factory and simply brought out four wires: 12V, ground and two motor wires.

When it's used in the application we're discussing (i.e. signaling to a controller), that wiring scheme won't work. Because the two normally closed (NC) contacts are shorted together inside the enclosure, the diodes are needed so that the other two switches (on the sticks) can't pull the "up" and "down" lines low simultaneously through the RS-2's shorted NC contacts.

Notice also that when it's used this way, the wire that normally carries 12V to the switch (and is connected to both normally open contacts), is instead wired to ground; thus, the "motor" wires only connect to ground when the normally open contacts are closed by switch activation. The wire that normally ties to ground (and shorts both NC contacts) is left unconnected.

The other wiring option (and the one I would choose, if I were installing an RS-2) is to open the back of the switch case and re-wire it to function as a SPDT switch (see Diagram 2 on the last page). Much less fiddly than trying to add diodes to a wire bundle.

All clear as mud now?

[alexM]

32843
Yep, totally clear now. I obtained the RA switch as a package deal with the RA LED trim indicator. I had read that the Kitfox toggle switch was, uh, "less than durable" over the long run, so I had intended to go with the RA and TCW Safety Trim.

[Eric Page]

I had read that the Kitfox toggle switch was, uh, "less than durable" over the long run, so I had intended to go with the RA and TCW Safety Trim.
In signal-level service, the Kitfox switch would probably outlast the airplane. I obviously have no first-hand experience with a failed Kitfox trim switch, but my guess is that the problem with it is contact wear related to back-EMF from the motor. Since the switch has to operate the motor in both directions, it's not possible to protect its contacts with a diode across the motor like you normally would. Either orientation of the diode would short the drive current in one direction or the other. It's not really a problem with the switch Kitfox selected; it just lives a particularly hard life.

[Geek]

In signal-level service, the Kitfox switch would probably outlast the airplane. I obviously have no first-hand experience with a failed Kitfox trim switch, but my guess is that the problem with it is contact wear related to back-EMF from the motor. Since the switch has to operate the motor in both directions, it's not possible to protect its contacts with a diode across the motor like you normally would. Either orientation of the diode would short the drive current in one direction or the other. It's not really a problem with the switch Kitfox selected; it just lives a particularly hard life.

I'll pile on here too Alex. The stock Kitfox config has the whole current draw of the trim motor getting pulled through it. So the contract wear that Eric talks to is greater (read happens faster). If you are using the Safety Trim, then the current through the switch is dropped to mA vice Amps. Lot less wear and it gets you to Eric's "signal-level" service. Since I didn't use my panel switch, I'll be more than happy to give it to you.

Geek