Troubleshooting Trailer Brakes that Stopped Working

Updated 03/04/2026 | Published 12/04/2014

Products Featured in This Question

Dexter Electric Trailer Brake Assembly - 10" - Left Hand - 3,500 lbs

(312)

$81.82

Hook Probe Circuit Tester

(66)

$14.36

Question:

Just installed new brake kit on both sides of the brake axel. Adjusted the brake controller and had good brakes for about 300 miles and then suddenly no brakes at all, I still have running lights and brake lights and turn signals, but no brakes.

asked by: John B

Expert Reply:

There are a number of reasons why the brakes on your trailer may not be working. Lets start with the easiest things to check.

First, check the vehicle and trailer connectors for corrosion. This can cause a short inside the connector and the brake feed circuit and ground are at the bottom of the connector so moisture affects these connections first.

Next, check the ground wire on the vehicle and trailer connectors, trailer brake magnets and the brake controller itself. If there is a bad ground connection the trailer brakes will not work.

Next, check the brake controller wiring. Sever the blue brake output wire, leaving enough room to splice it back together when testing is done and then apply the manual slide. Using a circuit tester, like item # PTW2993, you should get output to the trailer brakes. If the manual slide activates the trailer brake output wire properly, try the brake pedal. If the brake pedal activates the brake output properly the problem is farther back either in the vehicle wiring or on the trailer.

If either the brake pedal or the manual slide are not functioning properly you will need to test the wires going into the brake controller. Make sure you have power entering the brake controller on the black wire and on the red wire only when the brake pedal is pressed. If these wires test correct, and there is no output, your brake controller most likely needs to be replaced.

I attached an FAQ on troubleshooting brake controllers for you to check out as well.

expert reply by: Jameson C

John

3/4/2026

hooked up a 6x12 cargo trailer worked the first day, hooked it up a couple of days later and truck indicates a wiring issue. trailer brakes locked up.

Jameson C.

3/4/2026

@John You probably have the 12 volt accessory circuit and the brake output circuit swapped and it's locking the brakes up.

John

3/4/2026

@JamesonC how can it get swapped one day to the next?

Jameson C.

3/4/2026

@John I misread your comment my apologies. If that's case it's probably a wiring that wasn't secured in the connector and it moving around has caused it to come loose and short to a different circuit.