Hi Guys,

I've recently purchased a 2013 ML350 Bluetec with 72ks on it. It seems to be in really good condition and I'm liking the car.

I need to add a tow bar for towing trailers and boats reasonable distances and through fairly steep passes, hence I'm very keen to fit a factory tow hitch system including the integration into the cars electrical system.

I found the motorised tow bars and thought they looked great and were rated at the upper limit for these cars which suits me perfectly. I looked at importing one before I'd done too much research, but eventually backed off the idea because of the associated shipping costs. Since then I found one locally including some extra parts for a very reasonable price and purchased it.

The tow bar purchase included the following:

• A166 310 01 04 - Motorised tow hitch
• A166 310 01 18 - long member left
• A166 310 02 18 - long member right
• A166 905 17 00 - Rear door switch
• A166 440 69 13 - wiring harness from towbar to tow controller module (I believe this part is region specific version of A166 440 70 13, but I'm not 100% on this)
• A166 900 03 01 - tow controller module

From my reading and research I need the following additional parts:

• A166 315 00 65 - Bumper foam
• A166 905 10 51 - drivers door switch
• A037 545 65 28 - plug for drivers door switch (I'm not convinced on this part, but I believe I need a wiring harness between the drivers door switch and the door control module but I can't find a corresponding part number.)
• A166 540 44 10 - Main harness from SAM to Tow controller unit
• A166 540 50 35 - Wiring harness (I'm not sure on this one, but it appears compatible with my vehicle based on my research and it could be the red plugged cable for the tow controller module)

The above research is based upon:

• https://mbworld.org/forums/m-class-w...ler-hitch.html
• https://mercedes.catalogs-parts.com/#{client:1;page:modification;lang:en;catalog:eu;se t_aggtyp:fg;wheel_class:car;classname:gl-klasse;modelname:gl+350+bluetec+4matic}
• My local Mercedes dealer

I have a list of additional parts I think may be required or be relevant:

• A166 540 14 03/A166 540 16 03 - Wiring harness (unknown purpose, I believe these are model variations of one another)
• A166 540 48 35/A166 540 49 35 - Wiring harness (unknown purpose, I believe these are model variations of A166 540 50 35)
• A246 900 55 01 - Tow control unit (as my tow control unit came with the tow hitch I don't think I need this one)

My local Mercedes dealer wasn't very receptive to helping me with this initially, and only through perseverance have I found someone there who is interested in giving me some help. They haven't retrofitted one of these and do not seem very enthusiastic about helping too much.

My car is factory fitted with the following options I understand are relevant to towing:

• 554 - PREINSTALLATION FOR TRAILER HITCH
• 915 - FUEL TANK WITH GREATER CAPACITY - VOLUME 2

My reading elsewhere indicated that 554 includes the larger radiator fan.

I've done some preliminary investigations in the rear of the car to look for existing wiring harnesses, and I haven't found anything. My main concern was removing the tailgate trims and not seeing anywhere to connect the rear door switch to. This would imply new cabling from the switch all the way back to a control module inside the rear of the car.

My questions are:

1. Has anyone successfully retrofitted a motorised tow hitch to there w166 model vehicle?
2. Does anyone have a complete list of parts required?
3. Does anyone have instructions for the installation of the new wiring harnesses?

I expect there to be some regional differences but I think I can manage those.

Thanks for the help all!

 

If you are going to be towing "trailers and boats reasonable distances and through fairly steep passes", I'd buy a vehicle that has a factory towing package. It will cost you twice as much to retrofit everything on yours than to sell it and buy one in a similar condition that has the factory towing package. Besides, even if you do all that work, you'd still lack things like the larger transmission cooler and the electronic coding like the ESP Trailer Stability Assist functionality, which would keep your transmission a lot cooler and quite possibly save your life one day if things get out of control.

 

Hi Diabolis,

There are not many of the ML SUVs in my region with factory tow hitches.

I've investigated the programming side also, and this isn't a major from everything I've read online along with my brief discussions regarding this with the local dealer.

The hard part appears to be the extent of wiring required for the factory towing hitch, particularly when compared to other aftermarket towing hitch providers.

Your reasoning regarding stability control and transmission logic are the same reasons I wanted to have the factory towing hitch installed.

From my reading there isn't a larger transmission cooler for these vehicles as part of the factory tow package (appears to be limited to larger fuel tank, larger radiator fan, altered transmission logic and the like).

I'm happy to be corrected.

Cheers,

 

So I found the correct wiring harness for the car (A166 540 68 08) which had to be back ordered as there were none available.

I've managed to wire in the harness as per the factory instructions, but I can't get the cover back on the front SAM unit (my vehicle is RHD).

It appears there is a way of removing the SAM unit, but I can't figure it out and don't want to pry to hard and break my one! Does anyone know the procedure for releasing the front SAM unit under the A pillar?

Cheers,

 

I can confirm the wiring harness part number above is correct for my car. Car has been programmed and the towbar tested.

 

Hi Guys,

I've been using the car for towing now for a while and noticed a couple of things I wanted to ask about and check they are normal.

1. When the trailer is connected, the blind spot warning no longer operates and comes up with a warning on the dash and the led's in the side mirror stay red. Is this normal?
2. My two trailers have LED lights and flat, 7 pin connectors. I use a Narva adapter to connect the trailers to the towing hitch socket. When the lights are used (i.e. I use the turn signals), I get a warning about the trailer lamps on the dash. Is this normal, or a programming issue?

Cheers,

 

#1 is normal. Can't speak to #2 other than to say that when I pull our RPod with LED lights I get no warnings about trailer lights and they all work.

 

Hey there I am in the US and looking to do this to my ML - Could not find one with a tow package - so Here I am trying to build one. I dont have the pre-installed wiring option on my car so. Ill need a harness. My local deal is not willing to play ball. You listed a couple of part numbers for the harness - where you able to understand the differences?

Also were did you get the factory install manual?

 

I struggled to get help out of the local dealer also.
One of the methods I used was to find a car which had the motorised tow hitch, and pretend to be the owner and say I needed a replacement wiring harness. I then supplemented this by suggesting parts numbers which they could check if they were correct for the vehicle.

The local dealer wasn't able to find the correct part number for me, I was just lucky I'd done enough homework to know which ones were incorrect, otherwise I'd have a pile of useless parts.

It took a german parts company to find the correct part number for me. They also sent me the installation manual to confirm it was the correct part number before I ordered. Send me your email and I'll send you the pdf.

According to the manual, the wiring harness inside the car is the same for LHD and RHD vehicles. (Assuming the same model specifications.)

 

Quoting so you see the reply above.