Activating 12-Volt Trailer Accessory Circuit on 7-way Trailer Connector of 2009 GMC Sierra

Updated 04/16/2016 | Published 04/15/2016

Question:

Im trying to trouble shoot the trailer socket for my 2009 gmc truck there are two wires in the front of my fuse box under the hood the one attached to the silver bolt has power and the one on the black bolt next to it doesnt on your Web site it mentioned something about a ground .there is a lose ground underneath the fuse box that is attached to the frame the other end is not attached to anything where does it terminate to ?

asked by: Eric

Expert Reply:

I'll assume you're doing some troubleshooting because the 12-v trailer accessory circuit at the trailer connector isn't functional.

There are two wires near the fuse box under the hood that sometimes need to be connected in order to power up your brake controller and the 12-v accessory power circuit to the trailer connector. To the right of the fuse box, next to the fender there is a red wire with a ring terminal on the end. It connects to the left hand power stud on the front side of the fuse box. This connection powers the brake controller. Under the brake booster/master cylinder, there's another red wire bundled up with a ring connector on the end of it. This wire delivers power to the 12-v accessory circuit at the trailer connector. To power the circuit up, connect it to the right hand power stud at the front of the fuse box.

I've provided a photo showing these connections, and I've also linked you to an FAQ article which explains this in greater detail.

expert reply by: Mike L