I've got a 2005 GMC Sierra that I need to install trailer brake control on. I've got the wiring harness that came with the truck. I've plugged it into "electrical center" under the dash, driver's side near the brake pedal. I plugged the 40 amp fuse into the "lug 1" in the fuse box. I still get now voltage out of the wiring. I put my volt meter on red and black and get no voltage. Is there anything that I am missing? Any other fuse or other thing that needs to be done to get the harness to work?



Thanks... Jason

not sure about "lug1"..i think it may be in the wrong hole...

I think it's called Stud 1... not lug 1.

When I purchased my '05 (used), the dealer gave me the "pigtail" to use with my brake controller. This pigtail plugged into the slot on the fuse panel for the 7 pin connector at the hitch receiver. I had to figure out the wiring of this pigtail to the pigtail for my brake controller. I spliced the wires together and hooked up the brake controller to the dedicated slot in the fuse panel.

My question to you: Is it possible that one or more of your wires are not in the correct position? I had a diagram to guide me, but it was about as clear as mud.

I hope you get it resolved soon.

Im in the same boat as your are,mines a 05 chev though. I did the same with mine, got the factory pigtail and wired in the controller. I also have no power to the red wire. Yes i put the 40 amp fuse in the stud #1 location.

I pulled that electrical center out from under the dash on the drivers side....out of the 4 wires, only 2 are hooked up! On mine i have the ground wire and brake light input wire. Im completely missing the main red power wire and the dark blue trailer brake output wire.

Im pretty sure the wire's are in the truck but just not hooked up to the electrical center under the dash.

I'll let you know what i find, hope this help's

I've got problems with my trailer brakes. I only get 7 volts out of my blue wire. Am I supposed to get 12. I can't find a bad fuse or bad connection anywhere. I've replaced the controller and harness under the dash. I can't figure in out.

Hey guys, sorry it took so long to reply.

So what i had to do was run a red and a blue wire into the cab. The red and the blue both connect/hook up to the brake controller on the inside of the cab ( obviously). Now under the hood, the red wire goes to stud #1. Thats why you have to put the fuse in.

And if you follow the wire harness that comes up into the bottom of the fuse panel thats under the hood, there should be a blue wire just sittin there, thats the wire you need to connect/ hook up to the blue wire you put in thats coming from the cab which is connected to the brake controller.

Now you can hardwire those two wires directly to the brake controller ( the red and blue) or like me, i went to local GM dealer and get the correct wire end terminals to put those two wires into the back of the panel that's by ur feet. I just did it cause i wanted it lookin factory.

And that should be it, provided you have a trailer plug in the hitch ;p


Now squares5,
Correct me if im wrong but you should get different voltage on that blue wire depending on how much you have the brake controller set at. I would think at full gain/output of the brake controller you should be putting out 12 volts on that blue wire. And the more you turn it down the less voltage you should get.

Unless the wire is damaged...are you getting 7 volts at the trailer plug? What about at the controller?

I got my problem figured out. The ground in my panel was not working. So I jumped my ground wire to the frame under the dashboard and Everything is working great.