Brake Controller Quit Working On 2005 GMC Sierra 2500HD

Updated 07/30/2020 | Published 02/15/2011

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ModuLite Installation Wiring Kit

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Hook Probe Circuit Tester

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Question:

my brake controller is not receiving power. it was and then was intermitant and now is doesnt light up att all. all my trailer lights work, but the brakes do not. like i said, the controller was working then stopped. all fuses are good under the hoodand the connection under the dash is good. i even replaced 7 way plug on trailer, nothing happened. the controller used to have a constant green on when the trailer is hooked up, but now has nothing. is there a different fuse or something else that is going on? thanks in advance. love the web site 2005 gmc 2500hd

asked by: Joe

Expert Reply:

I would check the power distribution box under the hood of your 2005 GMC Sierra 2500HD . The box is located under the hood and on the inside of the drivers side fender. Remove the cover, and locate the two auxiliary power posts on the inboard side of the box.

The post closest to the rear of the vehicle should have a red wire attached to it. Next to this post in the fuse box there should be a green 30 amp fuse installed. If the fuse is not installed or is blown, or this red wire is not attached, the brake controller will not get power.

There is another fuse you will want to check that is in the power distribution box. It is a fuse for the center high mount stop light (CHMSL). The diagram on the lid of the cover will show the fuse location. If it is blown it will not allow the brake controller to work.

Using a circuit tester like part # PTW2993, I would also recommend testing the wires under your dash that are connected to the brake controller. The black wire should have power all the time, the red wire only when the brake pedal is pressed, the blue wire should show power when the manual switch on the brake controller is turned on and when the brake pedal is pressed. I am including a video link of how to test the wiring on your brake controller.

Also, I am including a link to a FAQ page on GMC brake controllers that will show pictures and describe everything about installing a brake controller in your vehicle.

expert reply by: Jeff D

Steve S.

7/26/2020

I checked the wiring under the dash going to my trailer brake controller. And they al show a signal as they should, but the blue wire was a week signal.Any ideas about why that would be?

Chris R.

7/30/2020

It depends how you were testing that blue wire. That's the brake output circuit, so if you're testing it by stepping on the brake pedal and the truck/trailer is parked, it's not going to send back much power at all because the controller (assuming it's proportional) sends power back based on deceleration. Now if you're using the manual override on the controller and the voltage is still weak, that may be an issue. If that's the case make sure you have the settings bumped up on the controller itself and then test it again to see if it gets better. Let me know what you find.