Where to Attach a Red Trailer Brake Controller Wire on a Diesel Motor Home with Air Brakes

Question:

I have a diesel motorhome with air breaks. Under the floor is the break control valve and it has a few electrical switches connected to the valve body. I assume that one of these is the break light switch and can be hooked up to the controller... If this is correct, how do I find out which wire do I need to tap into. Can I connect to the break lights instead? That would be a major pain in the backside but Im trying to figure out if there is a way to install this controller or if I need to find a different solution. Thanks for any help you can give me.

asked by: Andrew N

Expert Reply:

It should be fairly easy to locate the brake light wire to install a brake controller. First check above the brake pedal. If there are wires there you can check that is the best place to start looking. If you have to tap into the control valve then you can test the electrical connections there.

In either case you will need a circuit tester like # PTW2979 if you do not already have one. Test the wires at either location. You are looking for the one that shows power to the circuit tester only when the brake pedal is pressed. If it also shows power with the turn signals or headlights on then it is not the correct wire.

Normally you cannot tap into the brake lights on the vehicle unless the brake lights are on their own circuit and not combined with either the turn signals or running lights. If there is a third brake light, you could tap into it in most cases. You can also tap into the stop light or CHMSL (center high mount stop light) fuse to get the brake signal to the controller.

expert reply by: Michael H