How to Determine Correct Brake Light Switch Wire for Brake Controller Installation

Question:

looking for where to connect the brake controller red wire for the brake signal

asked by: Max S

Expert Reply:

All trailer brake controllers use the same 4 wire hookup (white for ground, black for 12V power, blue for output to the trailer connector and red for connection to the brake light circuit). The correct wire on any vehicle to connect with the red input signal wire is the one wire at the brake light switch that carries power ONLY when the brake pedal is pressed and at no other time.

The easiest way to identify this wire is to use a probe circuit tester like # PTW2992 to test all of the wires at the brake light switch to find the one that goes "hot" only when the brake pedal is pressed. Use of the tester is shown in the linked video.

You can also refer to the linked article that covers the process of hard wiring a brake controller.

Another option is the find the circuit/wire for the 3rd brake light and to tap into this for the electrical "brakes on" signal needed by the controller.

expert reply by: Adam R