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Replacing Damaged 7-Way Trailer Connector on 2019 Mercedes-Benz 3500

Question:

Ok, I have a 2019 Mercedes SPrinter 3500 that came with factory towing wiring but the 7 pin receiver has been sheered off prior to my purchase and all I have left are the wire ends. The issue is that the wires colors do not match any replacement 7 pin/pole recieiver. I have heavier blue, red, white and brown wires and thinner green, yellow and pink, yes PINK wires. What I am lost at is if the factory wiring has a 7 pin receiver where is the black lead wire or where does the electric source come from? Id hate to rewire the whole thing when the wiring is there. I have contacted 3 Mercedes dealerships service and parts departments in the Atlanta area and none can help which I thought was odd!! Any thoughts

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Expert Reply:

I don't have the color codes, but you should be able to easily determine which wire colors carry which circuits by using a circuit tester like part # 40376.

Begin with the turn signals and running lights. Have a helper activate the right turn signal while you test each wire, chances are you'll find that the green wire carries the right turn signal. Activate the left turn, which is typically the yellow wire. Testing should confirm this. The brown wire usually carriers the running lights.

As for the remaining wires, the blue wire usually carries the output from the trailer brake controller, the red should carry a constant 12-V from the vehicle battery and the white is usually ground. The pink wire likely carries the reverse lamp circuit. I'll link to a help article that shows how a 7-way should be pinned out.

For a replacement 7-way, I'd go with the # HM40975-11998. The kit includes a 7-way/4-pole trailer connector, the wiring pigtail that would wire up to the existing wiring you mentioned and a mounting bracket. The wire color code on the pigtail is different than what's usually seen, I've provided a chart showing the color code.

Wiring Color Code for Trailer Connector Pigtail Included with HM40975-11998
Wiring Color Code for Trailer Connector Pigtail Included with HM40975-11998
(click to enlarge)
Customer Provided Photo
Customer Provided Photo
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expert reply by:
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Mike L

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