What Would Cause a Trailer Brake Controller to Lock Up Even on Lowest Setting

Updated 08/13/2019 | Published 08/12/2019

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Hook Probe Circuit Tester

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Question:

Trailer brakes lock even at lowest setting

asked by: Jim K

Expert Reply:

If your trailer brakes are locking up when you touch the brakes even on the lowest setting that normally indicates a short between a stop/turn circuit of the trailer lighting and the brake output that runs to the trailer brakes.

Normally if you inspect the wiring at the trailer connectors you'll find where there's a short and you'll be able to fix it pretty easily.

In some cases the problem could be a bad brake controller so here's how to test that.

Testing the brake controller is fairly easy. Sever the blue brake output wire near the brake controller leaving enough room to reconnect it and then apply the manual slide. Using a circuit tester like the Quickee Tester, part # PTW2993, you should get output to the controller side of the wire you severed. If the manual slide activates the trailer brake output wire properly, try the brake pedal. If the brake pedal activates the brake output properly also then the problem is farther back either in the vehicle wiring or on the trailer.

If either the brake pedal or the manual slide are not functioning properly you will need to test the wires going into the brake controller. Make sure you have power entering the brake controller on the black wire. On the red wire you will only want power when the brake pedal is pressed.

If there is power on the red wire before the brake pedal is pressed you have connected the red wire from the brake controller to the wrong circuit. You would then need to find the brake switch wire that has power ONLY when the brake pedal is activated.

If these connections check out and the brake controller is properly grounded then there is possibly a problem inside the brake controller.

I am including a link to a video that will show you how to test the wiring on a brake controller.