Brake Controller Not Working when Installed on a GMC Top Kick

Updated 11/30/2015 | Published 11/29/2015

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Question:

I found the brake light switch on the brake pedal, there were 4 wires in 2 plugs. I found the one that lit up the brake lights with my tester. It does not work the brakes on my trailer. Is there another wire that I shoul be using ? I have an activator II by drawtite. The little decimal light stays on when the truck is shut off. And there is a slide button on the side of the box thats marked sync. My trailer brakes are humming as soon as I plug into the truck which says to me theyre engaged.. I can not get the manual brake slide to have any effect on the LED screen. I can not get the output slide to do anything. The only thing that adjusts is the sync slide. Ive gone over and over and can not seem to get it. Any other things I need to do ? Ive hooked up other controllers with out any issues. This ones got me baffled. I did not do a bench test as I opened the box and started the install. The part in the directions where it talked about a bench test came after the installation section. Do I HAVE to take it all back out and do this test and re wire it all ?

asked by: Willie

Expert Reply:

No, you do not have to remove the controller to test it to see if it is the issue. There are some tests that you can perform to determine if the controller or something else is the problem.

In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # PTW2993 to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override. If it shows power at idle, then there is something wrong with the controller and it will need to be replaced.

If it tests fine then reconnect the blue wire. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.

You can test the brake output pin and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.

If the truck side checks out fine then it could be the wiring to the brake magnets or the magnets themselves. Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.

expert reply by: Michael H