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GMU 22 to GSU 25 wiring question

georgemohr

Well Known Member
Hi all!

Have a look at my proposed wiring harness between the GMU 22 in my left wing, and the primary GSU 25. The G3X install guide suggests that the cannon plug has two pins called "SIGNAL GROUND" (pin 1 and 3). My best guess here, since the book also calls for a 2-conductor and 3-conductor shielded wire, is that these two SIGNAL GROUND pins get routed to the shielding, and ultimately drained to the J252 connecter backshell on the GSU 25.

1) Is that right?
2) If so, is there any specificity about which SIGNAL GROUND goes with which conductors? I suspect not since they all get grounded together, but...

Thanks!
George
 

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Last edited:
1. Two cables each with the shield (labeled Signal Ground)
2. Terminate the shield for the cable to the pin shown in the G3X install manual.

In my G3X install manual it shows the RS-232 with the power wires and not with the RS-485 wires. You should double check that your drawing matches the Garmin recommended wiring.
 
GMU 22 connection

Here is a copy of latest (ap) G3X manual for the GMU22.
 

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Hi all!

Have a look at my proposed wiring harness between the GMU 22 in my left wing, and the primary GSU 25. The G3X install guide suggests that the cannon plug has two pins called "SIGNAL GROUND" (pin 1 and 3). My best guess here, since the book also calls for a 2-conductor and 3-conductor shielded wire, is that these two SIGNAL GROUND pins get routed to the shielding, and ultimately drained to the J252 connecter backshell on the GSU 25.

1) Is that right?
2) If so, is there any specificity about which SIGNAL GROUND goes with which conductors? I suspect not since they all get grounded together, but...

Thanks!
George

They are signal grounds for RS data lines. It is pefectly acceptable to use the shield for this ground, but it is not the same as a grd drain on an otherwise unused shield. THey should go to the signal ground pins on both sides, Not to a frame ground or backshell.

Larry
 
Here is how mine in wired from Stein's diagram on my -10
 

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