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Old 01-12-2006, 11:22 AM   #1 (permalink)
BenzWorld Junior Member
Date registered: Jan 2006
Vehicle: '02 C320 / '03 ML350
Posts: 8
Trailer Hitch Wiring

I have an '03 ML350 that I want to add the OEM trailer hitch / wiring. I have read through the various postings and it seems like a no brainer....however, the MB Service Rep I spoke to get a quote from ($1,050) says that my ML is not prewired. He stated that he will need to run power from the fuse box to the rear connector and the total labor is six hours.

Has anyone ever heard of this?
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Old 01-12-2006, 04:20 PM   #2 (permalink)
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Date registered: May 2005
Vehicle: Brabus ML 270CDI
Location: Basel, Switzerland
Posts: 1,904
RE: Trailer Hitch Wiring

Checkout the details on my webserver. (It's too much to post!... and I can't remember exactly where I got it from!!!!)

username: guest
password: w163

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Old 01-12-2006, 07:01 PM   #3 (permalink)
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Date registered: Nov 2003
Vehicle: '00 ML320
Location: Torrance, So Cal
Posts: 179
RE: Trailer Hitch Wiring

Power from the fuse box back. Why? The only reason you need to tap power when towing is for electric brakes. The ML isn't really wired for towing, but with the OEM towing wiring harness in becomes wired for standard towing or for hydraulic tongue brake systems.

To run electric brakes you need to tap power for the controller and run a line back. If the price includes everything (hitch, harness, installation, brake controller wiring, and controller) then it isn't too bad.

The is a TSB for installing a controller.
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Old 01-12-2006, 10:05 PM   #4 (permalink)
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Date registered: Oct 2005
Vehicle: '03 C240, '03 ML350
Location: Orange County, CA
Posts: 144
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RE: Trailer Hitch Wiring

JonhK - Just did the factory hitch install over the weekend on my '03. Mine was prewired and my SA said they all are. Just had to fish the terminating end of the harness out of the driver side rear trim panel. But it's there - plug-n-play. Before you spend the $, just look for it. The only real bummer about the install is having to cut the rear bumper to fit. I made the cut on the actual bumper, but took the trim cover to a bodyshop. They made the 80mm X 80mm X 170mm cut for $50. Even after the $295 cost for the kit and the $50 bodyshop charge for the delicate cutout, it was over $700 cheaper than the dealer. And it looks factory, which is all we ask for.
'03 C240 Sedan, Black/Java
'03 ML350, Black/Black
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Old 01-15-2006, 09:10 AM   #5 (permalink)
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Date registered: May 2004
Vehicle: 1994 C280 1996 C36 2002 ML500
Location: San Francisco, CA
Posts: 511
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RE: Trailer Hitch Wiring

I just installed the OEM hitch last week myself on my 2002 ML500 and like others have said it was easy although it did take a bit of time. Mainly busy work so nothing difficult. I was able to get the wiring harness in without removing the interior panel by sneaking it through a ventilation hole behind the bumper. There is a grille there but it pops off as it is just cliped at four points on the side. I purchased my hitch from the dealer for $295.

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Old 03-28-2011, 09:37 PM   #6 (permalink)
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Date registered: Mar 2011
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Talking 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.
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Old 03-29-2011, 07:16 AM   #7 (permalink)
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Date registered: Mar 2011
Posts: 2
Pics attached

Here are the pictures:
Attached Thumbnails
Trailer Hitch Wiring-bumper-covers-2.jpg   Trailer Hitch Wiring-bumper-removed-2.jpg   Trailer Hitch Wiring-wiring-harness-2.jpg   Trailer Hitch Wiring-wiring-harness-front-2.jpg   Trailer Hitch Wiring-step-6-2.jpg  

Trailer Hitch Wiring-wires-2.jpg   Trailer Hitch Wiring-hitch-receiver-2.jpg   Trailer Hitch Wiring-bumper-cut-2.jpg   Trailer Hitch Wiring-hitch-complete-center.jpg   Trailer Hitch Wiring-hitch-complete-right-2.jpg  

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Old 04-29-2011, 07:28 PM   #8 (permalink)
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Date registered: Apr 2011
Posts: 3
Hitch cover

Hi nice job I was wondering if you would be interested in parting with the body cover that you removed from the bumper where you installed the hitch, thanks Bill 609-868-2220
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Old 05-01-2011, 07:17 AM   #9 (permalink)
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Date registered: Mar 2011
Vehicle: 2003 ML500, 2003 C320 4matic
Location: CT
Posts: 12
Originally Posted by 2004ML3504X View Post
Here are the pictures:
Thanks for the great writeup, it was very helpful. I did the trailer hitch and harness install myself last weekend, and this thread made it a piece of cake. Total cost to me was about 180 bucks.

Last edited by Wolfie version 8.1; 05-01-2011 at 07:19 AM.
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Old 09-07-2011, 10:58 AM   #10 (permalink)
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Date registered: Feb 2011
Posts: 10
Thanks for the great step-by-step. Looks to be relatively uncomplicated. I picked up the U-Haul package this morning. If the weather isn't too bad I'll do the install on Friday. I have a couple of questions:

Did you cut the stock connector off?

Have you had any issues with the U-Haul system since you've used it?

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