Garmin G3x Wiring Questions

[Shadowrider]

Hey everyone! Working on wiring and my brain hurts! I am going to have lots of wiring questions so I figured I should start another thread instead of on the build log?


I am currently working on wiring up the gea-24, which is the box that all the engine senors connect to. The manual shows (I think) a 2 conductor wire coming from the CHT to the GEA-24. It is saying most of the sensors, other than the egts, need to have Garmin Shield block ground, which I assume is grounding the shield to the backshell? Also with lots of sensors needing to be grounded to the backshell do you just start stacking the grounds? Lastly it shows the 2 conductor wire going to each CHT. One as the signal and the other grounded to the aircraft. It is showing the ground to be on the end where the CHT probe is? Not sure what you do there? Is it okay practice to run a single shielded wire from the CHT probe to the GEA-24 that then the shield is grounded at the backshell of the GEA-24, and then run another shielded wire from the GEA-24 for that CHT to the ground bus for the aircraft?

Sorry I know there is a lot of questions there, any input would be helpful!

[Flybyjim]

Hi Dustin,

After reading the manual setup I had the harness made for my whole G3X system, this is one area I felt it was better to have someone build it that did it every day. I used Steinair for this service.

Jim

[Shadowrider]

I know the feeling! Seems like I need to just hire someone to come out and wire it all up for me🙂

[Flybyjim]

Steinair was a great company to work with, very patience and helpful. I am going to be painting this fall and hope to fire up the panel before year end.

[efwd]

Don't be fooled by the belief that the shop has people who do it everyday. You might be surprised, as I was. Go with Stein Air. They sponsor this site too.

[Shadowrider]

Hi Eddie! Yeah I think I am going to charge forward trying to figure this out. Looking back I think I would have gone with AFS or Dynon pre-wired panel from Stein Air. I feel like I am too deep to look back now. Eddie did you run your CHT sensor wire to the probe? The drawing has me to believe the CHT probe is grounded next to the probe itself on the engine, but I dont see why I can't ground the sensor at the ground bus bar coming from the GEA-24?

[efwd]

Hey Dustin, I couldn't offer any advice because the 912iS has all that stuff wired already. I just had to get a "pig tail" harness to bridge from the engine harness to the ECU. I only had one sensor to wire and that was the fuel flow sensor. Sorry I couldn't help. I get it, I would wire my own stuff if I do it again. I don't much care for the fit of my harnesses.

[Shadowrider]

Next question is the audio from the G3x. Is the mono for warnings and stereo for music? I am guessing I should hook up both just trying to understand what each one is for?

[PapuaPilot]

Next question is the audio from the G3x. Is the mono for warnings and stereo for music? I am guessing I should hook up both just trying to understand what each one is for?

Don't over think this part, but I think you are correct. Just hook the audio up as depicted.

[Shadowrider]

Don't over think this part, but I think you are correct. Just hook the audio up as depicted.
Thanks. Trying not to....

Is there a good help line for garmin? I am guessing I better program that number in my phone!

[efwd]

Garmin Support 866=739-5687

[Shadowrider]

Next question. Seems like I read somewhere in the 900 page manual, does the G3x need permanent 12v power?

[PapuaPilot]

No, it doesn't need any kind of keep alive power.

Most of the LRUs have 2 pins so you can power it from 2 sources if you desire.

[Shadowrider]

No, it doesn't need any kind of keep alive power.

Most of the LRUs have 2 pins so you can power it from 2 sources if you desire.

Thanks! My "reading" is not so bad.........my "recall" not so good:)

[Shadowrider]

Who knows the gtx45R? From what I am gathering, RS-232 (1) is used for GSU-25(adahars) RS-232 (2) is for the GDU 4xx (G3X touch screen). Do I just use RS-232 (3) for the GPS 20 input?

I guess what I am asking is I am running the GPS-20, which is providing wass gps signal to the transponder. Isn't the transponder going to use waas gps position and altitude from the transponder? So do I still provide info from the GSU-25, which is providing altitude via static pressure?

[PapuaPilot]

I'm not totally sure I understand all of your questions, but this may help.

The GPS-20A is your WAAS GPS source required for ADSB-out position and possibly IFR navigation. It's not the altitude source for the transponder as GPS altitude is not overly accurate. The altitude source for the transponder/ADSB and the display(s) (GDUs) comes from the ADAHRS (GSU-25). The GSU-25 provides pressure altitude, which is corrected using the altimeter setting and is very accurate.

I'm not sure how all of these hook up and communicate with each other with the GTX-45R. I have a different transponder. My GPS-20A connects directly to the transponder using a RS-232 channel and sends its data on the CAN bus too. The CAN bus connects to both the GSU-25 and GDU-465. Therefore using both the CAN bus and RS-232 the WAAS GPS position is provided to the entire G3X system.

You are going to need to look carefully in the installation manual chapters 26 and 27 to find the answer to this.

[Shadowrider]

I'm not totally sure I understand all of your questions, but this may help.

The GPS-20A is your WAAS GPS source required for ADSB-out position and possibly IFR navigation. It's not the altitude source for the transponder as GPS altitude is not overly accurate. The altitude source for the transponder/ADSB and the display(s) (GDUs) comes from the ADAHRS (GSU-25). The GSU-25 provides pressure altitude, which is corrected using the altimeter setting and is very accurate.

I'm not sure how all of these hook up and communicate with each other with the GTX-45R. I have a different transponder. My GPS-20A connects directly to the transponder using a RS-232 channel and sends its data on the CAN bus too. The CAN bus connects to both the GSU-25 and GDU-465. Therefore using both the CAN bus and RS-232 the WAAS GPS position is provided to the entire G3X system.

You are going to need to look carefully in the installation manual chapters 26 and 27 to find the answer to this.


Thanks! Back to reading....

You understood my question\s perfectly. I was assuming the GSU-25 was not needed because I thought WAAS altitude is more accurate than pressure altitude and it seemed kind of silly to provide pressure altitude to the transponder when it already had more accurate altitude provided by the GPS. But sounds like in this configuration its not as accurate so altitude is provided by GSU-25.

So I found on the FCC website the installation manual for the GTX45R that is version 2. Garmin only list version 1 on their website??? So anyone installing a GPS20A and a GTX45R or here is the interconnect drawing. Also if you are wondering what the A/c Suppression BUS is? Answer listed below.


Thanks for your help PapuaPilot. I am running the GTX45R transponder and it does not appear to have a CANBUS connection. I am assuming that the GTX45R communicates to the G3X via the 232 that I hook up to it. Seems weird there is no canbus to it?

Also once you have the GPS-20a connected properly does it provide position source to the G3X if I am not running anything else like a GTN650 or GNS430/530 ect?

Last thing to figure out. I think the GPS-20a can provide gps position to my ELT? Next thing to figure out. I need to dig into the ELT next but maybe the external suppression is used?

The EXTERNAL SUPPRESSION is intended for connection to other L-band equipment, such as a DME
or UAT. The output is active whenever the GTX 35R/45R transmits. When driven by another source, the
GTX 35R/45R transponder receiver and transmitter functions will be suppressed.

22812

[PapuaPilot]

Happy reading. The GTX45 is certainly different than my GTX23ES.

[PaulSS]

You understood my question\s perfectly. I was assuming the GSU-25 was not needed because I thought WAAS altitude is more accurate than pressure altitude and it seemed kind of silly to provide pressure altitude to the transponder when it already had more accurate altitude provided by the GPS. But sounds like in this configuration its not as accurate so altitude is provided by GSU-25.

Transponders work off 29.92 and then 'fudge' the result to get altitude. It would be no good providing a GPS altitude because (a)they're not as accurate as you think and (b)they're not working off a standard pressure setting, so everyone can be off by varying amounts. So you definitely need to provide your transponder with a pressure-based altitude, instead of GPS-based. Since the EFIS is plumber for pitot and static pressure it's quite normal to just have the transponder 'talk' to the EFIS over the CAN bus and gain the information it needs from there.

[tracstarr]

I currently am installing the GTX45R with the same equipment as you mention. Here's what I have...

GTX45R >>> G3x
30 41
8 24
51 35

GTX45R >>> GSU25
31 9
9 10
52 11

GTX45R >>> GPS20A
29 5
50 6

G3X >>> Artex 345 ELT
48 9

[Shadowrider]

Transponders work off 29.92 and then 'fudge' the result to get altitude. It would be no good providing a GPS altitude because (a)they're not as accurate as you think and (b)they're not working off a standard pressure setting, so everyone can be off by varying amounts. So you definitely need to provide your transponder with a pressure-based altitude, instead of GPS-based. Since the EFIS is plumber for pitot and static pressure it's quite normal to just have the transponder 'talk' to the EFIS over the CAN bus and gain the information it needs from there.

Thanks for your response. Just for the sake of discussion I thought the WAAS GPS was more accurate then anything? It gives you true altitude very accurate. For example I can get lower on the approach on most WAAS gps LPV approaches than i can via ILS. Vertical guidance is provided by gps alone. Maybe garmin protocol is not there yet. Or the other idea is maybe they are running two sources of altitude on the garmin transponder for redundancy?

[Shadowrider]

I currently am installing the GTX45R with the same equipment as you mention. Here's what I have...

GTX45R >>> G3x
30 41
8 24
51 35

GTX45R >>> GSU25
31 9
9 10
52 11

GTX45R >>> GPS20A
29 5
50 6

G3X >>> Artex 345 ELT
48 9

That what I am getting also. Only difference is I went GPS-20a to ELT (ACK) via GPS-20A RS232 TX 2 (pin 3 on GPS20).

I also installed the, Made in China, super pain to put pins on, USB cable. Seriously..... can't we just put a USB port on the transponder???

RED pin 44
Green pin 2
WhT pin 24
BLK Pin 45

Interesting side note, I accidentally turn on elt for about 2 seconds. Hurried and called the command center and they said they just saw ELT trigger for a couple seconds. He had me read them my HEX number and it was my ELT. That was in my shop they said they got a hit and next pass of the satellite would have given location. Crazy! I apologized and he thanked me for calling.

[PaulSS]

Thanks for your response. Just for the sake of discussion I thought the WAAS GPS was more accurate then anything? It gives you true altitude very accurate. For example I can get lower on the approach on most WAAS gps LPV approaches than i can via ILS. Vertical guidance is provided by gps alone.

The GPS altitude is certainly getting better day by day and it is, in some cases, super accurate as you say. Regarding the approaches then an ILS may well have higher minimums due to surrounding terrain, strange topography etc, whereas a GPS approach can 'steer round' that terrain and allow for a more customised approach and lower OCL.

The trouble with the transponder using GPS altitude is the standard of GPS used. Some people may have a super-duper all-singing and dancing bit of kit, whereas others may have a cheaper one that doesn't self-check, allow for RAIM outages etc. Many people won't even have a GPS coupled to their transponder. And there's the problem: ATC can't provide separation if pilot A has a magic machine providing extremely accurate altitude information, pilot B has a cheapo GPS chip from eBay and pilot C is still working off static pressure being fed to his encoder. Since we're not there yet with a standardised GPS altitude we have to stick with what is currently in place i.e. every transponder working off 29.92 inMg (1013.25 Hectopascals) to give your flight level and then a 'fudge' calculation made by the ATC machine to provide your altitude (below 18000' in the USA).

As for pins, don't get me started :-) I'd bought loads of Dsubs, pins and the crimping tool only to find 18AWG won't fit and I wasn't happy with cutting of strands of wire to make them fit. SO, I bought another load of Dsubs with solder cups. My soldering is really not very good (although I have got better over the last few days), so it was a struggle trying to ensure pins didn't get soldered together etc. I started with a female Dsub and, looking at the back, the pins run 1 to 9, left to right. All good and soldering done. 3 female Dsubs later and it's time for some male Dsubs. THIS complete idiot assumed the numbering would be the same.......it's not, as most sensible people will know. 5 DSubs male Dsubs later and suspicion is roused by something I read. Damn you to hell Google for revealing my mistake. Shrink tube, solder, wire, molex connectors which looked so neat...........:(

My top tip is to get a permanent pen and write the numbers on the back and front of every Dsub before picking up the soldering iron :o

[Shadowrider]

Whats the deal with config module? The little black box smaller than a dime? Why does it have funky pins and how are you suppose to connect them? I can't find instructions in the manual?

[tracstarr]

Whats the deal with config module? The little black box smaller than a dime? Why does it have funky pins and how are you suppose to connect them? I can't find instructions in the manual?
Not sure I know what you are talking about. Do you have a picture?

[Shadowrider]

Not sure I know what you are talking about. Do you have a picture?

I am guessing these pins to solder on because the wires are so small you cannot crimp them? Wondering which way you solder them on? Also looks like there is a mounting hold and a screw to mount this somewhere?


https://lh3.googleusercontent.com/3vrP8J8eeWxpo-j-8dQEijtg8nHun8NDWuvjRDk2hmuJodeWDm68Rjs404CHJsh3c8 SdGi_hzc-12t99g690dRlH_rbPFe4R7lvuEe_92oF-4MjjpQSQWRPYfzUFHngAGLZFxiDWMVw=w800

https://lh3.googleusercontent.com/vnSO1xgnf1xDFmERDN9oEIWRp58Q-wQLYkRzLk5aVYkoBrC8-NWRJx6575QEi-khte5Vu0dMCumxecTHvUxx468SVi7WR0-cftzEEeJeKZJ6uOlHLFmMdBOxsMT9sBkhAbbmcIUI3lY=w800

[tracstarr]

Well that's a new one to me. I don't have that. Hope I don't need it. I'm not quite ready to turn everything on yet. Another week or two.

Sent from my SM-G973W using Tapatalk

[Shadowrider]

Well that's a new one to me. I don't have that. Hope I don't need it. I'm not quite ready to turn everything on yet. Another week or two.

Sent from my SM-G973W using Tapatalk

I think is saves configuration and it has a clock so I am pretty sure you need it?

22837

[PaulSS]

They are the same pins as Dsub pins. You need a Dsub pin crimping tool, similar to this:

https://www.steinair.com/product/4-way-indent-crimper/

Just Google Dsub crimping tool and you can watch a video on how it is used.

[efwd]

I have that very crimper. I works well. Bad thing was, stripping wire that small caused me to have to buy another wire stripper that had that gauge. Back to the device. I don't have anything like that for the G3X. The closest thing I have is the one that goes in my Transponder connector. It was more of a chip encased in epoxy, not black. It does hold information that the transponder uses to identify you to ATC.

[Shadowrider]

They are the same pins as Dsub pins. You need a Dsub pin crimping tool, similar to this:

https://www.steinair.com/product/4-way-indent-crimper/

Just Google Dsub crimping tool and you can watch a video on how it is used.

Yes I have that tool. These have different pins than all the rest of the connectors? Garmin only gave 4 of them so I was wondering if these are solder pins. My elt I tried to crimp with this tool and the male dsub would not hold the wire on because the wire was so small of wire I had to solder them.

[Shadowrider]

I have that very crimper. I works well. Bad thing was, stripping wire that small caused me to have to buy another wire stripper that had that gauge. Back to the device. I don't have anything like that for the G3X. The closest thing I have is the one that goes in my Transponder connector. It was more of a chip encased in epoxy, not black. It does hold information that the transponder uses to identify you to ATC.

hmmm......It shows it in the installation manual and says there is details to install the configuration module in chapter 20 but cant seem to find more info on where this is suppose to mount. I am going to go back and check transponder because I did not see anything like you mention on my transponder. I have the GTX45R.

[Shadowrider]

22838

Just found this.

[efwd]

Interesting. I don't recall ever seeing that but it is likely that when the avionics built my harnesses, they had removed all the connector stuff from my boxes already. The only reason I recognize what it is is because I had to replace mine when Garmin took my radio back to do a software change. When I got my radio back I was instructed to swap this device that was in the connector. Let us know when you figure out where it is to be installed.

[Shadowrider]

22839

I found it. It goes in the big harness that connects to the back of the G3X. The pins they supplied are dsub pins but made for the very small wire is what I am guessing as the hole where you put the wire in is much smaller than the other pins supplied by garmin. That makes sense Eddie thanks. After reading it sounds like it stores configuration of each LRU connected via can bus. It says when you power up the LRU it basically downloads configuration for the LRU from this device is the best I can interpret.

[PapuaPilot]

I didn't have time to reply till now, but I have been able to see all of the responses throughout the day. I'm glad you figured this out because you need to have the configuration module installed in the connector for the system to work.

Making the wiring harnesses for the G3X (or any other brand) is not an easy task. Even if you chose to wire the rest of your plane doing the avionics installation is so much more complex as we are seeing here. Honestly, I would say this is going to be the most difficult and demanding part of the entire build. Realize, if one component is missing, mounted wrong, has the wrong wiring or a reversed /missing / in the wrong hole pin it is not going to work. It will be a PITA to find the problem as well as lots of time talking to tech support. When you power up the system you could smoke something and ruin your new equipment. Warranty won't cover it.

Do you really think you want to install and wire your avionics? The easy part is choosing the combination of whiz bangs you are going to put in your panel. If you are thinking about doing your own harnesses you will need to read, read and read all of the manuals, but you need to understand them too. You need to grasp the big picture as well as the smallest details. It is a huge learning curve. You will need to purchase lots of expensive tools that you will probably never use again. You will need to figure out lengths, types and sizes of wiring, all of the connectors, etc. that you will need. And about another million other things. This is a job for a detailed person who loves puzzles.

BTW I did make the harnesses for my G3X system, but:
I was able to borrow all of the required tools where I worked
I have been working as an A&P for a long time, including a bit avionics stuff
I had flown with the G1000 panel and understood the big picture of the system & components
I was able to do most of the work at our avionics shop
I had a couple of full time, highly experienced avionics techs to ask questions. They routinely do Garmin installations.

I hope other builders will read this thread before they decide to make their own harness. In most cases it would be best to purchase them from a reputable avionics shop. Even if you hire it out you will need to decide on what your complete package will be and the exact location for every component . . . before they can start.

FYI we had a wiring problem with a Cessna Caravan this week where I work. A couple of our highly experienced avionics guys spent (lost) 3 days troubleshooting an autopilot problem. It ended up being a pair of wires that got reversed during a upgrade that involved wiring. Before they figured out the problem they were considering replacing all of the servos . . . $$$, and it would not have solved the problem.

[Shadowrider]

Thanks Phil, all good points. I am working on wiring up the trim switch. I have the gsa-28 servos and the safety trim switch. Trying to understand the wiring diagrams. Looks like I wire the switch up just like in the manual but instead of the power coming from 12v bus, it’s provided by the safety trim switch? So pin 2 from the safety trim box to the switch like drawn? And then blue lines go to pin 11 and 12 on servo?
22856
22858

[Shadowrider]

Thanks Phil, all good points. I am working on wiring up the trim switch. I have the gsa-28 servos and the safety trim switch. Trying to understand the wiring diagrams. Looks like I wire the switch up just like in the manual but instead of the power coming from 12v bus, it’s provided by the safety trim switch? So pin 2 from the safety trim box to the switch like drawn? And then blue lines go to pin 11 and 12 on servo?
22856
22858


just to follow up, this is how to hookup trim to a saftey trim switch and the gsa-28 servo. At least this is how I did it and it works.

[Shadowrider]

Does anyone know if the stereo outputs from the G3X only provide music to an audio panel/GTR20 if you pay for the xm music? All the alerts come from the mono output correct? I am debating on unhooking the stereo outputs from the g3x that go to my GTR20 and connecting them to my ipad so you can have audio from the ipad to both headsets? Anyone see a problem doing this?

[tracstarr]

The gtr20 has dedicated line in on 18,19, 37 for music.

[Shadowrider]

The gtr20 has dedicated line in on 18,19, 37 for music.

Yes. I guess I worded my question poorly. I used the GTX to GTR20 interconnect drawing. It shows music out form the G3x (pins3 9 20) and music in from 19 18 37. I was wondering what this is for? Read more and found this is if you opt for the xm music. It comes from the G3X. Audio alerts come form mono G3x out to the mono GTR20 in.

So I am going to disconnect pins 3 9 20 and hook those to audio jack that goes into my ipad. Audio alerts will still work over the wire I ran from the G3X pin 1 and 18 to pins 32 31 on the GTR20.