How to Test a Brake Controller for When Brakes Lock Up all the Time

Question:

Hello, I installed this unit on my old motorhome to brake a tow dolley with a 2400 pound car on the dolley.It worked normally. I traded in the old rv and I bought a new one.It is a 2014 Ford f-53 rv chassis with a factory installed trailer brake harness. I moved the brake controller to the new ford chassis RV. My problem is with any brake application on the RV I get instant brake lock up on the tow dolleyroad master. I turned the primes setting no boost down to 2.0. No change, the tow dolley brakes lock up with the slightest brake application. I did a voltage test at the trailer harness and I got 8 volts with brakes lightly applied on the RV. What voltage should I be getting from the primus controller?

asked by: Peter H

Expert Reply:

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 part # PTW2993, 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