I'm having a problem getting brake lights to work on the trailer plug on my 2002 Sierra K1500.Truck lights all work fine with independent turn and brake lights. The previous owner butchered whatever was there for the trailer from the factory and just left wires hanging down. I can get everything to work on the trailer except brake lights, although both turn signals work. I get no power on the turn signal wires when the brake pedal is applied, but do get power on a light blue wire in the wiring harness (not the trailer brake controller wire). Tried adding two different converters and no difference.None of the after market harnesses Í"ve found seem to have the connections to match what the truck has. Any more suggestions from anyone?

 

Seems to me you can just take a 12v wire off of your brake lights, and pipe it into the trailer connector to be used for your brakes.

I've never wired a trailer plug before, so it's possible that I'm not correct. There could be another better way to do it.