Boat trailer running lights won't work on new GMC AT4HD

[cjacksonlasd]

UPDATED POST:  2021 32 FT BOATMATE TRAILER RUNNING LIGHTS NOT WORKING.

New 2025 GMC AT4 HD.  Running lights on 32ft 2021 BOATMATE Trailer won't turn on.  Repairs done so far:

1) New 7 pin Plug - No change in Lights.
2) Bought 7 Pin plug tester, all lights light up corresponding test light with no issues.
3) Purchased Furrion Camera Adapter plug at recommendation of others, when turning on truck, the running lights work for about 2 seconds, then they shut off and I hear a humming start from the Furrion Adapter.
4). Purchased another Adapter at recommendation on Amazon, no impact at all.  Twice while testing with it, I saw the LED lights go on for a blip only, could not reproduce results.
5). Running Lights turn on fine in my Dodge Durango.

I feel the issue must be the truck or some combination.  The lights work fine on Dodge Durango, and they light up for a second on the GMC, and tester shows the GMC lights are sending power, can't figure out what is causing this .

[64BAwagon]

There may be a fault in the trailer lighting circuit that the trailer module doesnt like. They are very sensitive. 

 

[PhilB]

Just a thought - have you tried covering up the light sensor on the dash so that the truck thinks it is dark out?

 

Have you tried connecting a different trailer to your truck to see if the running lights work?

 

When I connect my bass boat trailer to my truck, I use the trailer light test either on the app or on the infotainment screen to test the lights.  Have you tried that?  

 

Another thought - most boat trailers use the hitch for the ground.  The ground wire from the plug was just stubbed out. I had issues with the trailer lights once so I ran another ground wire from the plug to the body of the trailer to ensure a good ground connection.  As mentioned by 64BAwagon, the trailer module is sensitive.  A bad or weak ground could cause the issue.  

 

 

[ManyCamaroz]

Have you connected a clean 12v source to each of the trailer plug pins to check each light circuit on the trailer itself to verify the issue is not with the trailer?