No Power On Blue Wire to Trailer Brakes from Brake Controller

Updated 05/12/2015 | Published 05/10/2015

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Question:

I have no power to trailer brakes. I have the brake controller wired but still nothing to trailer. We have a good ground and have power at black wire. But blue wite coming out of controller doesnt have much amperage.

asked by: Dalton K

Expert Reply:

To cover the easiest things first, make sure that the brake controller output or gain is turned up. If the power is low then the voltage on the blue wire will be low. When testing for voltage make sure to use the manual override and not the brake pedal. On many proportional brake controllers the vehicle has to be moving for the brake controller to send back the proper voltage via the brake pedal.

Also make sure the controller is mounted within its range specified in the instructions and not tilted or turned to the side.

You can also test to see if the brake controller 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.