Trailer Wiring 7-Way 12 Volt Circuit Troubleshooting for a 2008 GMC Sierra Duramax

Question:

I have a 2008 GMC Duramax with intergrated brake contoller. My 12 volt pin on the 7 way does not work. I have read the forums and cannot locate any additional wire under the master cylinder other than the red/black stripe that is already attached to one the the lugs on the front of the fuse block. FIrst question, is this red/black stripe wire the correct wire for the 12v? The reason I ask is because I traced it to the back of the truck and had 12v up to the fuel tank and nothing behind the fuel tank. I spliced in another wire before the fuel tank to the red/black strripe wire at the 7 way plug. I now have 12 volts at the pin in the 1 oclock position on the 7 way. However when I start the truck I have a message to Service Trailer Brakes. Now I am wondering if that wire has something to do with the integrated brake controller but cant understand why the red/black stripe wire would be on the 7 way in the 1 oclock position. Please help!

asked by: Gary D

Expert Reply:

To rule out the wiring you connected to the 12 volt pin as the reason for the service trailer brakes message you are seeing you will want to disconnect that wire and reset your truck computer by disconnecting the negative side of the battery for 10 minutes to clear the code. If the code clears then you know the reason that code popped was because of that connection.

If you need 12 volts on that circuit and can't find the correct circuit an easy solution would be to get a length of 10 gauge wire like part # 10-1-1 and connect it to the positive side of your vehicle battery, run it to a 40 amp circuit breaker like part # PK54540, and then run that wire to the 1:00 position of your 7-way. This will bypass your factory wiring and would eliminate the possibility of causing codes to pop. And will eliminate any guess work.

expert reply by: Jameson C