Trailer Brake Controller Installation in 2005 GMC Sierra

Updated 04/02/2018 | Published 03/31/2018

Question:

I have a 2005 GMC Sierra and recently installed a trailer brake controller. I purchased the wiring harness designed for my truck to be a instant plug and play. I have a 7 pin plug in the back for a RV that is plugged directly into the factory harness for trailer lights. The controller is not getting power. I checked the fuse under the hood, it’s good. I check led all fises under the hood and inside, they’re all good. Am I missing a step? I’ve researched and tried fixing this for the last 3 days and I can not find a solution. Please help

asked by: Jamie M

Expert Reply:

I do not know which controller brand and model you have or which wring adapter you're using. But for reference I linked our range of controllers, such as the Prodigy P3 # 90195, confirmed to work with the 2005 Sierra with factory 7-way. This controller uses wiring adapter # 3015-P for installation in your truck.

I linked an article to help you. This covers the whole process of brake controller installation in your truck. The article calls out in the second section the two wires, red and blue, that must be connected to the nearby electrical posts at the power box under the hood. These wires are shown clearly in the photos in the article. Normally these are connected at the factory on trucks with a factory 7-way, but it is possible this was not done on your truck. Fuses are also needed as shown in the article; make sure yours are fully inserted.

Sometimes what can happen during installation is that the wrong port under the dash is used to connect the controller. If you refer to the first section of the article, which covers the install in trucks that have a factory-installed 7-way, the photo at right shows the truck's under-dash junction box, which is located on the driver's side below the dash, to the left of the brake pedal. The correct place to plug in a brake controller harness is the second port, highlighted in red. I linked this photo separately too to make it easier to see.

On rare occasions the pre-wired adapter harness may be mis-wired, with wires going to the wrong pins or having pins in the wrong slots on the connector. It does not happen often but it does happen.

expert reply by: Adam R