Trailer Brake Controller Not Applying Trailer Brakes on a 4-Car Trailer  

Question:

Expert Reply:

It could be the controller, or it could be a problem between the controller and the trailer brakes. The easiest thing to try first is to check the vehicle and trailer side connectors for any dirt or corrosion. Make sure they are clean inside and out.

To test the brake controller, you will start by severing the blue wire a few inches from the back of the controller. Then use a circuit tester such as # PTW2993 to test the end of the blue wiring coming out of the controller while fully applying the manual override. The test light should light up when you do this test. If it does not or if it shows power all of the time, then there is something wrong with the controller and it will need to be replaced.

If it does work as it is supposed to then re-connect the blue wire. Next you will need to trace the brake output wire from the back of the vehicle side connector forward on the truck as best you can. You are looking for any brakes in the wiring or areas where it may be pinched and thus won't have the best connection.

On the trailer side, make sure the main trailer connector ground and the magnet grounds are attached to clean and corrosion free bare metal surfaces. Check the power wire from the trailer connector to the magnets and fix any broken or loose connections.

You will also need to make sure the brakes are properly adjusted. You want to adjust them so that there is a slight but constant drag on the drum.

I have included a couple of links on testing and troubleshooting brake controllers for you.

expert reply by: Michael H

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