Trailer Brakes Not Working when Using Brake Pedal

Updated 09/16/2015 | Published 09/15/2015

Question:

Lights on trailer are working. The emergency brake switch also works. When I apply brake pedal I hear buzzing sound at axles on the trailer. I picked trailer up off the ground and free spin the wheels 4. When I spin wheels backwards brakes work very little, but when I spin them forward they free spin again.The trailer is less than 2 years old.

asked by: Billy M

Expert Reply:

It sounds like the problem is with the brake controller or the wiring to the brakes. But first, many proportional controllers need to sense forward movement to apply the trailer brakes with the brake pedal. So if you are sitting still that could be the issue.

Try it with the manual override instead of the brake pedal. If the brakes work fine, then it may not be the controller. It may not be the wiring either, but it could be that the brakes need to be adjusted.

If you suspect the controller is the problem, there are some tests you can do. 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.