Brake Controller Troubleshoot on 2005 Ford F150

Question:

When using the manual lever, I get a proportional voltage reading at the trailer blue wire from 2 to 12 volts. When I push the brake pedal, I get a voltage from to to 3.65 volts max. There is a device rheostat? with a plunger that goes in and out at the top of the brake pedal as the pedal is depressed. Does this devicecolored blus and white vary the voltage as the pedal is depressed? There is also a device that is connected to the pin that connects to the brake booster rod. What is the function of that device? When I moved it with the key on it give a short reading or an overload reading on the controller. Thanks for any help you can give me.

asked by: George F

Expert Reply:

There is not a rheostat in the controller, but there is an inertial sensor that senses how quickly the vehicle stops, and then sends the appropriate voltage to the trailer brakes. The variable voltage you read when using the manual override will depend on how high the output on the controller is adjusted. The small amount of voltage you get when the brake is pressed is actually the voltage the controller sends to verify that the trailer is connected. The controller will not send full voltage to the trailer brakes when depressing the brake unless the vehicle is in motion. The red wire on the controller ultimately connects to the brake stoplight switch above the brake pedal. This circuit goes hot when the brake pedal is pressed, and is an on/off signal which tells the controller that the vehicle brakes have been activated.

expert reply by: Mike L