How to Wire a Brake Controller to a Vehicle that has Unknown Wiring Colors

Published 05/05/2016

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Question:

The black unit has a white wire .. a black wire a red wire and a blue wire..... the wiring harness has a white wire with a red stripe a green wire with a black stripe ...A Grey big wire last a grey wire with a white stripe.. which wires go to which wires to make the unit work?

asked by: Chuck

Expert Reply:

Sounds like you are trying to install a brake controller in a vehicle that has different color wires for the brake controller install wiring than the standard colors that your controller has. Since I don't know what vehicle you have it's hard for me to say which wire is which. But I can help you test them to figure out which is which.

Using a circuit tester like part # PTW2993 you will need to test the wires for voltage. The one with voltage all the time is the 12 volt power which goes to the black controller wire. The one with power only when brakes are applied is the stoplight switch and goes to the red wire of the controller. That leaves the ground wire and the brake output circuit.

Ground the tester to the constant 12-volt power wire, then probe the remaining two wires. The wire that lights the tester will be the ground, the other will be the brake output circuit.

expert reply by: Jameson C