Brake Controller Applies Trailer Brakes When Headlights are Turned On

Updated 01/04/2010 | Published 01/01/2010

Question:

My system works fine until my headlights are on and then the brakes activate as though you applied brake pedal. I have a gmc sierra 1500 2000 model and am plugged in box under dash. I have auto headlights. Any ideas?

asked by: Richard T

Expert Reply:

The first thing to check would be to make sure the brake controller is in the right port on the block underneath the dash. It should be the second port from the left on the top row. I have included a link to the instructions for your particular truck.

It is possible that your truck did not come with the appropriate wiring to the rear of the vehicle. If the brake controller is in the correct port and it still does not function properly, then you will have to hardwire the brake controller according to Steps 3 and 4 in the instruction file I have included a link to.

It is also possible that the trailer or vehicle is wired incorrectly and has the taillight signal swapped with the brake controller signal on the 7-Way connector. I have included a link to a page with a 7-Way trailer connector diagram. Make sure your vehicle and trailer follow this pattern. You can use a circuit tester like part # 40376 to check.

If you have any more problems, let us know what you find and we will trying to help you further.

expert reply by: Patrick B