Trailer Brake Lights Do Not Work After Installing Trailer Wiring on a 2006 Mercedes E350 Wagon

Question:

Installed the following module #C59496 and all the lights work except the brake light. It appears the tail and stop lights are on the same circuit. I tapped the red into this circuit and grounded the brown as per the instructions. But still no brake lights..?

asked by: Rob

Expert Reply:

When you tested the tail light wiring to perform the installation did you come across a wire that was just brake but also a wire that was both brake and turn signals? If so then the wire that has both functions would go to the yellow wire on the left side and to the green wire on the right side and the red wire would be grounded with the white wire.

You could also try using the brown wire in place of the red wire and ground the red wire.

If none of these solutions works then try moving the ground to a different location. Instead of testing with a trailer, make sure to test the 4-Way end on the vehicle to see if it the harness or the trailer. If it is the harness and no wiring configuration works then the harness should be replaced.

If it is the trailer be sure to check the grounds for all the lights, the trailer connector and inspect the wiring to the lights.

expert reply by: Michael H