I have a 2003 H2 and was not getting trailer brake signals to the 7-way plug on bumper. I learned that the dealer not only used the port under the dash for brush guard ligjts, they also used the circuit #47 known as "trailer auxiliary supply voltage" to feed the power for the lights through the firewall. After hunting for a single wire plug above the front left wheel well, known as plug c105, I saw there the blue factory wire they disconnected and replaced with a wire going to the lights on the brush guard.

After unplugging my brush guard lights and plugging back in the factory wire, my trailer brakes worked flawlessly.

I hope this saves someone else the 3 hours I spent having to chase this down.

 

Thank you so much for this. I had the same issue. Plugged the blue wire back in and everything works. You are a lifesaver. 👍🏻

 

if you wire in a 5 pin relay you would be able to toggle between the 2 functions. wire what you want to be default on, to the normally closed part of the relay and the secondary function to normally open pins

 

Awesome, thanks again.