Testing a Brake Controller and Trailer Wiring for a Trailer with the Brakes Not Working

Question:

I have a dual axle trailer with electric brakes. Only two years old. 6 months ago the brakes worked fine. Tried it a few days ago, nobrakes. Controller and slide seems ok. I have running lights and turn signals. I did notice the wire from the break away switch plunger to the tongue had broken.

asked by: Tony R

Expert Reply:

The way the brake signal gets to the trailer brakes is from the controller to the 7-Way, through the breakaway system, and then to the brakes. Since the breakaway system wire is broken that could very well be your problem so I would check that first.

To check the brake controller, sever the blue wire a few inches back from the controller. Use a circuit tester like # PTW2993 that you referenced to test the end of the blue wire coming out of the controller. It should show power on that blue wire when you apply the manual override on the controller. If it does not, then make sure the controller is receiving power on the black wire. If it is, then there is something wrong in the controller and it will need to be replaced. If the controller is not getting power, then check the wiring on the black wire and any fuses/circuit breakers related to powering the controller.

If the blue wire is getting power as it should go back to the 7-Way without the trailer connected and test for power from the controller. You will need to have one person test and one person operate the manual override on the controller. If power does not make it back, then there is a problem somewhere in the wiring leading back to the 7-Way.

If power is making it back, then the issue must be on the trailer. Connect the trailer and test for power on the 7-Way behind the trailer side connector. Keep testing working your way back until you find where the power no longer gets through. I have also included a link to our FAQ on testing brake magnets should you determine that power is getting back to the brakes.

expert reply by: Michael H