Continued testing fuse block, breaker and wire connections. Note: Skipped GTR discrete 1 and 2, pilot and copilot PTT and headset and mic jacks since they were previously tested. Connections tested were:
GAP status.
Seat Heat power for pilot and copilot.
Start active.
Pmag power and enable right and left.
Ignition switched and ground.
Master switch and ground.
Starter ignition switch and ground.
Trim power circuit breaker, GAD 27 pitch and roll trim motor power and trim switches from pilot and copilot. I temporarily connected a trim motor for the test. I thought I would be able to use the G3X "trim" menu in the configuration mode to move the motor, but found out I had to use the pilot/copilot controls. I assume the "trim" menu will work after I complete configuration and connections for the GSA autopilot. I also spliced one of the trim power motor wires that was damaged (probably before I received the wire).
Switch and power to the aft power port.
Strobe, NAV/POS and Taxi right and left switches
Landing light connections including switch to GAD 27, Light power to the GAD 27, and GAD 27 power to the landing light wires.
Flap motor power to the GAD 27, flap switch connections to the GAD 27 and GAD 27 power to the flap motor. I noticed that the GAD 27 applied a 8 to 10 volt signal to the flap motor wires even if the flap power circuit breaker was open if the wires were not connected to a load. I confirmed that a load of a small trim motor would not move unless the flap power circuit breaker was closed.
Fuel pump power and switch.
Pitot heat power and switch.
GNX to ELT RS-232 signal using a scope. Also spent time reviewing and testing other RS-232 signals between the GNX, G5, GDU and GSU. I don't think I was able to confirm all of them.
Alternator Field Breaker.
Alternator current sensor and battery current sensor wires to the GEA by connecting a Hall effect sensor. The power wires to the panel were looped through the Hall effect sensor twice and I could verify operation by turning the G5, GNX and GTR and verify the current changed.

I continued troubleshooting two issues and am ready to send an email to Garmin support.:
GAD 29 CAN bus connectivity: I am unable to see the GAD 29 on the device list on the GDU. There is an "A429" in the list, but the box does not have a green check or a red x and the LRU information is not displayed. The GDU shows 0% network errors. The GAD 29 status led is blinking green which is supposed to indicate "On and communicating using the CAN Bus". I did notice that the green status LED on the GAD 29 starts flashing immediately when power is applied. The green status LED on the GEA, GAD 27 and GSU turn green when power is applied, but don't start flashing until about 20 seconds after power is applied to the GDU 460. I disassembled the J291 connector and verified the pinout was correct for the CAN-H and L signals. I made a temporary J291 connector that only had power. When I connect it to the GAD 29 the status LED illuminates to a solid green and does not start flashing.

When I go to the GDU configuration mode "Engine & Airframe" page I see 4 tabs: GEA 24 inputs, GEA 24 discrete, GAD 27 inputs, and Settings. I have been able to go to the input and discrete tabs and configure and calibration inputs and in many cases see the status of the input so I can test the wiring. Sometimes I see an input that I was previously able to configure and see blue text which means I can select it and change it. Other times I see an input that was I was previously able to configure (I can see the name I assigned) that is displayed in white. When that happens, I am unable to select it by touching it or using the knobs. I saw this when the Garmin LRUs were running the original software (purchased Fall 2022 and all received by Jan 2023). I updated the G3X LRU's with the latest software and now I only see this issue on the "GEA24 Discrete". I've only rebooted a few times so I don't know if the issue with the other tabs is really resolved or not.

I updated software on the G5 and the GNX375 after I updated software on the G3X LRUs.

I am also going to ask Garmin about a "GNX 375 needs service." "Transponder has failed." error message.