jdlae2504s

I am considering getting a trailer hitch for my wife’s car. Per U-Haul, I understand the trailer wiring harness is special for her car. She has a 2009 ML350. I will install the hitch myself. What is so special about the wiring harness and installation? I received a quote from the dealer only selling the hitch, harness and installation - no breakouts. I was surprised how much they want...

Thanks in advance.

06e320cdi

check ECSTuning.com, they have rear SAM and what looks to be OEM hitch.

'93 300ce

Just a caution about anyone touching any wiring on your ML. Not everyone is aware of or has experience installing their own equipment on a Mercedes, even U-Hall. They were not aware of the adapter plug for the factory installed tow package with LEDs. Before I rented a trailer I went in to confirm they carried the plug adapter that worked with my LEDs they said they did but when I went to pick up the trailer and it didn't work their first instinct was to trouble shoot the wire connections and pull it a part. I had to prevent them touching anything.

The guys at San Diego trailer knew what I needed and carried the adapter in stock and it worked without a hitch ( or in this case with).

jdlae2504s

Thanks for the feedback and help.

N_Jay

The red light up adapter from U-Haul ($13) worked fine on my '08 GL (Factory tow package).
The ML and GL wiring is (or should be) the same.

Barney @21

I have an ML 350 V6 Build date 11/06.
I have purchase the Hitch harness from the Benze dealer here in Australia, it is the correct one for my Vin #.
When I went to fitting it there is no receptical for the over centre plug to connect to the SAM unit there are the places but there is a plastic cover over the hole and it has nothing under it.
The dealer tells me that my car was not built to tow a trailer.
.
Is it possible to buy a SAM to replace the one I have or will there be other connective issues?
Is it possible to buy an alternative loom /wiring system to enable a trailer to be attached ,I dont need trailer brakes.
Thanks

Maj. Dundee

You should always ask questions before purchasing parts. To retrofit the Trailer hitch it requires the replacement of the rear SAM (as you know) and a special Cooling Fan.

Barney @21

Thanks for your info.
I did actually try to get all the info , even the dealer said they had not come across this exact situation before. They suggested just changing the SAM may not work as the replacement may not talk to the rest of the sytem?? I was hoping to just pick up the affected circuits ( Tail /Stop / Blinkers) at the fuse ???. My car has coventional globes , Trailer has LED , my thoughts were that the SAM would not register the additional lights as the current draw would be so small??
Thanks again for your input.

Tsumi

Many people have replaced the rear SAM to the newer version without issues. It just needs to be programmed properly.

As for the LED trailer lights, what will most likely happen is that you get a warning that the trailer light is out and hyperflashing. To counteract that, you can get an adapter that cancels the error. Similar to this:

lkchris

what is “special” is that this vehicle has a CAN bus electrical system rather than a conventional electrical system. This means everything is computer controlled. For example single filament bulbs are used as both (same bulb) tail and brake lights. Computer sends 5v for tail, increases to 12v for brake. Can detect burned out bulb and substitute another.

one doesn’t “tap in” anywhere on a CAN bus.

Tsumi

While true, there are aftermarket solutions that can tap into those outputs and relay the correct signals to the trailer. The true benefit of going the OEM route is activating the car's trailer sway control and transmission tow mode. Depending on the year of the car, the integrated trailer brake controller can be utilized as well.

rmassmann

Maj. Dundee
The WIS for the OEM hitch that you posted on ( 12-03-2021 ) was very enlightening, but I am trying to add a hitch to my 2012 ML350 BT, which is a 166, how would I get copies of the WIS for it. It also looks like there may be an additional wire harness that I may need, was looking at ECS TUNING web site which sells a complete hitch kit for my vehicles and it is show an extra wire bundle that I do not have. I will get the mechanical completed, but would also like to the electrical element completed as well?

Bob Massmann
2012 ML350 BT

Maj. Dundee

Give me a day or 2.

Maj. Dundee

This retrofit will require the dissembling of half the vehicle. And it will put a huge dent in your bank account.

rmassmann

Maj. Dundee,

Thank you for the work instruction. It is really very involved isn't it. As I traded my only car with a trailer hitch and would prefer to use the ML for my trailer hauler, at this point I am sort of committed. I have most of the items to complete the job, but still need to find the second wire harness that connects to the cars electrical systems. I did find the trailer control module is still available through MB maybe the cable assembly is available too? I have found an alternate harness that only requires inductive pickups being added, but if I want to add a heavier trailer, I sure would like to take advantage of the car making adjustments based on what connected to it.

Bob Massmann
2012 ML350 BT

lkchris

There is more …

If the vehicle has Airmatic, automatic suspension lowering at highway speed will not occur if trailer is detected.

Status of trailer lighting will be monitored and messages appear on dash if a bulb is defective.

Tsumi

I consider those to be minor benefits as compared to the sway control and transmission behavior. But yeah, you are right, those are additional benefits.

Our R500 got 12-13 mpg pulling a 23' boat. That's the same mileage our 5.7 Ram MegaCab gets empty.