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.

D-Sub_Pin.jpg IMG_1661.JPG

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.

IMG_1659.jpg

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.

IMG_1660.jpg

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.

D-Sub_Crimped.jpg

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.

IMG_1663.jpg IMG_1664.jpg

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.

IMG_1668.jpg

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.

IMG_1670.jpg

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.

IMG_1671.jpg

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.

IMG_1672.jpg

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

IMG_1673.jpg

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.

IMG_1674.jpg

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.

IMG_1675.jpg IMG_1677.jpg
IMG_1678.jpg

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.

IMG_1679.jpg IMG_1680.jpg

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.

IMG_1681.jpg

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.

IMG_1683.jpg

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