Check trailer lights message

[jjoshj]

I had the same issues above, tried fuses and even a new trailer control module, nothing worked until I took apart the wiring harness going into the trailer control module and found a shorted and corroded wire. The copper had disintegrated. Spiced and used waterproof butt connectors and now working again without error. 

[OneToFixIt]

Wow That's amazing you found the bad wire.  How did you do that?  Seems like a bad wire could be anywhere in the miles of wiring.

Our 2022 Denali XL with 35k miles has been at the GMC dealer 5 times now for trailer wiring issues.  We have 2 trailers that behave exactly the same way (right blinker not working).  Both trailers work fine with a different tow vehicle.
Truck is giving many errors, such as "Check Trailer Brake Lamps" "Brake Gain Not Recalled" and "Check Trailer Right Turn Signal Lamp".  The truck passes with the GM simulated trailer plug (LED lights).

But when hooked up to any real trailer, the right blinker does nothing.  Right brake light does nothing.

Perhaps this is also a bad wire like yours but how would anyone ever find a bad wire???

[GMCustomerService]

3 hours ago, OneToFixIt said:

Wow That's amazing you found the bad wire.  How did you do that?  Seems like a bad wire could be anywhere in the miles of wiring.

Our 2022 Denali XL with 35k miles has been at the GMC dealer 5 times now for trailer wiring issues.  We have 2 trailers that behave exactly the same way (right blinker not working).  Both trailers work fine with a different tow vehicle.
Truck is giving many errors, such as "Check Trailer Brake Lamps" "Brake Gain Not Recalled" and "Check Trailer Right Turn Signal Lamp".  The truck passes with the GM simulated trailer plug (LED lights).

But when hooked up to any real trailer, the right blinker does nothing.  Right brake light does nothing.

Perhaps this is also a bad wire like yours but how would anyone ever find a bad wire???

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[Ntbgmc]

On 3/17/2025 at 9:54 PM, jjoshj said:

I had the same issues above, tried fuses and even a new trailer control module, nothing worked until I took apart the wiring harness going into the trailer control module and found a shorted and corroded wire. The copper had disintegrated. Spiced and used waterproof butt connectors and now working again without error. 

I have 2 wires corroded and need to do the same thing.  Did you cut the entire connector off and resolve everything or just the affected wires?

 

[Ntbgmc]

3 minutes ago, Ntbgmc said:

I have 2 wires corroded and need to do the same thing.  Did you cut the entire connector off and splice everything or just the affected wires?  My corrosion goes right up to the harness