How To Tell If You Have A Faulty Brake Controller

Updated 09/16/2025 | Published 05/17/2017

Products Featured in This Question

Tekonsha Prodigy P3 Trailer Brake Controller - 1 to 4 Axles - Proportional

(6644)

$156.06

Hook Probe Circuit Tester

(60)

$12.41

Question:

My trailer started locking the brakes up, I found out one problem was the plug in my bed but I have one in my bumper also so tried it and the brake box light is working properly now, but still having issues with the brakes wanting to lock up. Been researching your q and a and with the trailer unhooked I have the same reading on the blue wire as I do the black coming out of the brake box, so does that mean the brake box is bad on the power side? I leveled it and followed instructions on the power and level adjustments.

asked by: K B

Helpful Expert Reply:

The blue wire coming from the brake controller to the trailer brakes is the brake power output wire used to tell the trailer to apply the brakes once given the response from the brake controller. Therefore, you should not have a constant charge to the blue wire, except when the brakes are applied or the manual override is engaged on a proportional brake controller.

To test this you will want to sever the blue wire about 6" back from the brake controller then apply the manual brake slide and test for power. You should only see power on that wire with the manual override or brake pedal engaged. If there is constant power running through the wire then you have a faulty brake controller and it will need to be replaced. Use a circuit tester like part # PTW2993 to test for power as you apply the brakes in the vehicle. You may also want to consider testing the red wire which will give the same signals as the blue wire if functioning properly. If not, you know the wire is connected to the wrong circuit.

The black wire running to the back of the controller should always have a constant 12 volts. If you find the brake controller is bad, I recommend the Tekonsha Prodigy P3 Trailer Brake Controller part # 90195 as this is one of our most popular and reliable controllers.

If the brake controller is functioning properly, then there may be a problem with the wiring on the truck or at the trailer end connector. I would look for any sections of wire that may be pinched or frayed causing power to jump circuits.

expert reply by: Conner L

Richie

9/15/2025

The trailer still have lights but it’s no power going to the brakes. Trailer battery good. And the trailer brake away not applying brakes once the break away box is disengaged. Could the trailer brake controller affect the break away.

Jesse M.

9/16/2025

@Richie The brake controller should not affect the breakaway. Does your breakaway have its own separate battery? Or is it wired to the main trailer battery? If you are sure the battery is good, it is likely a wiring issue.