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'02 C320 / '03 ML350
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Discussion Starter · #1 ·
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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'00 ML320
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217 Posts
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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'03 C240, '03 ML350
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147 Posts
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.
 

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1994 C280 1996 C36 2002 ML500
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517 Posts
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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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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Pics attached

Here are the pictures:
 

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2005 ML500, 2002 E320 4-Matic wagon
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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?

Thanks,
Mike
 

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2005 ML500, 2002 E320 4-Matic wagon
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20 Posts
...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)...

U-Haul Color / Mercedes Benz Color
Green / Pink
Red / Orange
Yellow / Green
Brown / WhiteBlack (battery) / Blue/Green

...
Just an FYI: It took me two days to figure out either an error or a difference in factory wiring on my 2005 ML350. The Uhaul BROWN goes to the Mercedes THICK RED. My tail lights/running lights were getting less than one volt from the white MB wire. Used the multi meter to test the other wires in the plug block and the thick red wire on the lower left of the plug (with the open sockets facing you and the wires on the back). Also I didn't cut the wires but rather I found some crimp on male spade plugs that fit the factory plug. Crimped the plugs and used shrink tubing to keep it neat.

Mike

NOTE: THE PHOTOS SHOW THE BROWN WIRE IN THE INCORRECT POSITION. PICS TO SHOW USE OF MALE SPADE PLUGS


 

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'01 ML 430
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21 Posts
Power Module Failure?

Any suggestions on how to verify if the power module is working? I've had the DrawTite module-Lite trailer package for a number of years - and it has worked fine. This summer I noticed the boat trailer lights weren't working. Hooked the trailer up to another truck and they worked. So the problem is in the ML wiring, not the trailer.

Took a voltmeter to the 4-plug trailer connector, turned the lights on, and did not detect any voltage drop. Figured the 4-plug connector was corroded, even though I tape it up over the winter. So I snipped off the 4-plug connector and measured the exposed wires - again no signal.

So now I'm thinking the module went bad. Any ideas on how to test or other suggestions to follow-up on? The module looks like it is an integral unit - didn't see any way to open it up?

Thanks.
 

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2003 ML500
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2003 ML 500 W163 install complete

This thread made it a piece of cake to identify the wires. We used a Curt 56146 which cost $33. This comes with wire taps, but you will need an additional two. One for brown ground and one for red power wire. Get the next size larger one for the power since it is a thicker gauge.

As for the install. The ground wire was not attached to the chassis. Make sure to cut the ring off of the ground wire and the butt connector off of the black power wire. We tapped into one of the brown wires on the harness. There are two of them. The last and most important thing to remember is that you have to make sure you have a 25A fuse in slot F18 which is for trailer power. The fuse box is on driver side of engine bay. Label the wires on the Curt harness to the corresponding Mercedes wires to make hookup easier.

Curt Wires on harness >> Mercedes

Yellow >> Green = L turn signal
Green >> Pink = R turn signal
Black >> Red = power (+12V from fuse #18)
Brown >> White = tail lamp
Red >> Orange = stop lamp (and brake control)
White >> Brown = ground (negative from chassis)
 

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2005 ML500, 2002 E320 4-Matic wagon
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20 Posts
Hooked the trailer up today and the lights weren't working properly. The module was hot a slightly bulged in the middle. Haven't used it since September and it worked fine then. I'm really fed up.
 

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ML 430
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8 Posts
Hello,

I have ML 430 1999.
Can I connect electric wires from hitch direct to the ISO connector on car, or my car needs universal electric module like U-haul?
I will towing only yet ski.
Thanks for your answer.
 

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04 ML350, 04 E55 AMG
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27 Posts
Anyone that is getting a hitch should try to find an OEM Mercedes hitch kit, made by Oris. It took me 3 months to find one, but was worth it because the wiring harness is plug and play and the frame reinforcements are of higher quality. Just got mine installed. The worst part is cutting the plastic cover to fit the hitch, I could have done a better job.

 

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2005 ML500, 2002 E320 4-Matic wagon
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Part number?

Does anyone know how to find the part number for the factory harness from the empty plug back to the trailer plug. I've seen a few different part numbers that all claim to fit what I have now which is a 2005 ML500.

Thanks
 
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