Wiring a Brake Controller to an RV on a Sprinter 3500 Chassis Pre-Wired for a Brake Controller

Published 12/09/2016

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Question:

trying to determine if my 2016 Prism by Coachmen MB Sprinter 3500 is prewired. looked under the seat and there are two wires marked brake control. one large blue with white tracerbrake signal wire? and one small Orangebrake light switch wire?. The is a third wire connected to what looks like the fuse blockyellow with black tracer. I have installed brake boxes before. How do I preceed. Will be towing an electric brake car dolly for my car behind the motorhome, also what brake box do you recommend. Thanks

asked by: Scott C

Expert Reply:

It sounds like your Sprinter chassis does have the wiring for a brake controller. A brake controller such as the P3 # 90195, which is an excellent choice and what I would go with, needs one wire for 12-volt power in, one wire from ground, one for output to the trailer brakes, and one for input from the brake switch.

It sounds like that fused yellow and black wire is the power wire and it would go to the brake controller black wire. One of the wires you found should only have power on it when you step on the brake pedal. use a circuit tester such as # PTW2993 or a meter if you have one to test those wires. Whichever one only has power when the brake pedal is pressed is the one you will need to attach to the brake controller red wire.

The other wire is likely output to the trailer brakes and would connect to the brake controller blue. That leaves only the white ground wire on the controller. There may be a ground location under the seat or another wire. The ground has to be substantial though so the best place to ground a brake controller is the negative battery terminal if at all possible.

expert reply by: Michael H