Troubleshooting Brake Controller that Locks Up Brakes When Brakes are Applied  

Question:

Expert Reply:

It sounds like one of your stop/turn signal circuits has shorted out to your brake output circuit on your truck's trailer wiring and when you touch the brakes they end up locking up. You can test this by turn on your blinkers with the trailer connected. If the brakes on the trailer lock up with either blinker then you know that circuit is the one shorted to the brake output circuit.

You can also use a circuit tester like part # PTW2993 to perform this test. You would just need a friend to apply the turn signals while you have a circuit tester probing the brake output pin of the connector. Corrosion on the inside or outside of the connector and exposed wire can cause this.

Testing the brake controller is fairly easy. Sever the blue brake output wire near the brake controller leaving enough room to reconnect it and then apply the manual slide. Using a circuit tester like the Quickee Tester, part # 3808, you should get output to the controller side of the wire you severed. If the manual slide activates the trailer brake output wire properly, try the brake pedal. If the brake pedal activates the brake output properly also then 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. On the red wire you will only want power when the brake pedal is pressed.

If there is power on the red wire before the brake pedal is pressed you have connected the red wire from the brake controller to the wrong circuit. You would then need to find the brake switch wire that has power ONLY when the brake pedal is activated.

If these connections check out and the brake controller is properly grounded then there is possibly a problem inside the brake controller.

I am including a link to a video that will show you how to test the wiring on a brake controller.

expert reply by: Jameson C

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