Finding the Brake Switch Wire to Install a Brake Controller on a Sprinter Van

Updated 05/11/2016 | Published 05/09/2016

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Question:

Found the wire harness under the driver seat on sprinter chassis. I have a constant hot,but none of the other wires are hot when brake pedal is pressed. Not sure if it needs a fuse or relay somewhere

asked by: Mike T

Expert Reply:

It could need a fuse, less likely that it would need a relay but you can check the fuse panel lids to determine if there is one that is missing for brake controllers, tow package wiring, CHMSL, or stop light.

If that is not the issue then you would want to do things the old fashioned way; tapping into the brake switch wire that is hot only when the brake pedal is pressed. It is possible that the wire is a black/purple wire. On newer models it is a pink/green wire. I still recommend testing with a meter such as # PT89ZR since a circuit tester that uses an incandescent bulb might not be able to detect the low current (amperage) on some Sprinter brake switches.

expert reply by: Michael H