Date registered: Mar 2011
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2004 ML 350 Trailer Hitch Wiring
I just installed a hitch receiver for a 2004 Mercedes Benz ML350. I have included detailed instructions on how I installed it, including the wiring (U-Haul wiring kit Part# 13493). Please note, the wiring described below is for informational purposes only. If you are unsure or uncomfortable working on your vehicle, please take it to your local authorized Mercedes Benz dealer to have it installed for you. The setup below is strictly to tow a trailer with no brakes (power for the lights, brake lights, left and right turn signals, running lights), as I will not being using a trailer with additional brakes. Total time (being a first timer, about 3 hours).
1) Open up your hood and on the drivers side locate the fuse box. Install a fuse in #18.
2) On your rear bumper, remove the three panels (two small ones) and the one large one in the center to access the 4 bolts (10mm socket) required to remove the bumper.
3) Stand in the center facing the bumper and it should slide out towards you if you pull on it gently on both sides.
4) On the driver's side, near the gas tank, locate the two vent boxes. Prop them open with a flathead screwdriver (they have 2 clips on each side holding them in place).
5) Locate the prewired wiring harness. Some wires are thicker than others (specifically the orange. you will be using the thinner ones below). The colors reflect the following:
Green = L turn signal
Pink = R turn signal
Gray = backup lamp
Red = power (+12V from fuse #18)
White = tail lamp
Orange = stop lamp (and brake control)
Brown = ground (negative from chassis)
Blue/Green = ignition (power lights)
6) In the middle of the two vent boxes, I scraped the paint off to have access to the metal beneath it. I tapped into it using the white wire from the U-Haul Power Module to act as the ground wire to the vehicle.
7) I installed all the wires in #8 below, into the wiring harness and tested out the trailer to ensure all the lights were working correctly.
8) I matched up the following wires from the U-Haul Power Module to the Mercedes Benz Wiring Harness. I cut the wires from the MB Wiring Harness and crimped the wires together using butt connectors as I didn't have the MB connector.
U-Haul Color / Mercedes Benz Color
Green / Pink
Red / Orange
Yellow / Green
Brown / White
Black (battery) / Blue/Green
8) Afterwards, I neatly placed all the wires into the rear compartment and taped it down so it doesn't rattle. I placed the left vent box in. With the vent box on the right, I cut a small hole and I fished through the connector to the trailer. I then fished it all the way through to the center of the bumper.
9) Install the hitch receiver with the 4 bolts, tightening to the specified torque. I replaced the bumper by sliding it in and holding it in place and noted a small 1" cut that had to be made so that it fit correctly. I cut the piece off and reinstalled the bumper, installing the four bolts.
Pics coming soon.