Troubleshooting a Trailer Brakes that Lock Up All the Time When Brakes are Applied  

Question:

Expert Reply:

It sounds to me like there is either a wiring issue between the brake controller and the trailer connector on the truck or the brake controller is bad. Since your trailer brakes lock up when you are connected to the truck, that would indicate that there is constant power on the brake output circuit.

The first step that I would take is to use a circuit tester with an incandescent bulb like our # PTW2993, to test the pin in the 5 oclock position if you have a 7-way trailer connector. If you have a 6 way trailer connector, then the brake output circuit may be either on the center pin or on the pin in the 10 oclock position. You may want to have the truck running to ensure there is full voltage on all circuits. If you have constant power on the 5 oclock pin on the 7-way connector, then move to the brake controller.

For the 6-way connector, there are two common ways to wire a 6-way trailer connector. The differences are the pin locations for 12 volt power and the electric brakes. Make sure your trailer 6-way connector is wired the same way as the 6-way connector on your truck.

Moving to the brake controller, it should have 4 wires coming out of the back. White for ground, black for 12 volt power from the battery, blue for brake output to the trailer and the red wire should be connected to the cold side of the brake switch. Cut the blue wire about 6 inches back from the brake controller and test the wire on the brake controller side with the circuit tester. If there is constant power on the blue wire, then the brake controller may be bad. If there is no power, then make sure the brake controller is wired correctly.

You should have constant 12 volt power on the black wire and the red wire should only show power when you step on the brake pedal.

If the brake controller is wired correctly and you still have constant power at the 5 oclock pin on your truck, it may be possible that the trailer connector on your truck was wired incorrectly. The connector on your trailer could also be wired incorrectly. I have attached a photo showing the functions of each pin on a 7-way connector for you to compare to your trailer connectors.

Trailer connector adapters can also cause similar problems, especially if you are converting a 7-way connector to a 6-way. With the adapter plugged in, make sure the brake output pin on the 6-way side match up between the adapter and the connector on the truck or trailer.

I have attached three FAQ articles on brake controller installation and troubleshooting for you to check out. If you are unable to find a solution or the problem after following these steps, let me know what you come up with and we can take further steps.

expert reply by: Jameson C

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