flybd5

I need to locate and purchase qty 1 of the OEM trailer wiring adapter so i can plug in a 4-pin wiring harness from something like a U-Haul trailer to my ML550. The owner's manual describes it as a "four pole conversion plug" but as usual, there is no mention of a part number.

I bought what appears to be the correct adapter from a third party supplier but it gives me all kinds of grief. With the lights in auto the turn signals and stop lights work, but when I turn on the lights everything starts blinking. The dealer (Herb Chambers in Boston) claims that the adapter is not made anymore, but I think that's BS, it is impossible for that to happen when Mercedes is still selling vehicles with their OEM trailer hitch and plug.

Anybody know where I can get one? Any dealers here have one in stock?

jkaetz

Is it not simply a 7 round -> 4 flat adapter? Only problem I had with our 2011 is that it does not like LED trailer lights. That includes adapters with LED indicators. I had to make a short harness with some resistors to make the vehicle happy with our LED trailer lights.

flybd5

No, it's not. I've tried several types. The one from U-Haul blew my left front running light, took me two hours to replace that little @#*&#$ bulb. I would think that if it were the LED lights, the turn signals and stop lights would not work with the light switch in the vehicle in auto mode. It's only when I turn the lights full on that they don't work, just flash continuously.

flybd5

Argh, it is the LED lighting alright. I called MB customer service and after an endless litany of braindead recorded messages I finally got through to a nice lady to told me exactly what I needed to buy if I want to tow a trailer with LED lights.

http://www.etrailer.com/p-TR20141.html

You'd think Mercedes would have their proverbial caca together and take care of this in their computer...

Frank1298

This is what I used on my wife's ML550 and it work with no problems. My trailer has LED lights and this adapter is made just for that reason. http://www.etrailer.com/Wiring/Tow-Ready/TR20141.html

Frank1298

Yea when I used a regular adapter all I got was blinking lights and nothing worked. I order the adapter and tried and worked like a charm. i have used it 3x's since then with no problems.

CBR Dude

I'm using the adapter and have a new problem. Dash says trailer brake lights. It cured the flashing light problem!

I thought this was the cure all?

Thoughts?

flybd5

I guess it depends on which LED system is used. I'm not impressed that MB has designed this system so poorly. I just ignore it -- the lights on my trailer work fine.

sidewalkman

flybd5

$3,000 for OEM hitch means you can tow 7,000 lbs with the ML550. There isn't an after market hitch that can do more than 3,000 lbs. You get what you pay for.

CBR Dude

Plugging anything into the 7 pin socket will kill off the park assist and or the blind spot assist. Other wise the park assist would go nuts seeing the trailer.


Our Lexus when you plug in deactivates the parking assist, the blind spot assist the electric tail gate and a simulated vehicle pulling a trailer appears in the infotainment screen to remind you that you have a trailer behind you. All of this is outlined in the trailer towing section in the Lexus owners manual. But not Benz it's buried all over the manual.


Benz dealer was awful about the entire deal! Just plain lazy and uncaring. More like did not give a rats 2 cents about the issue!


The trailer shop did contact the manufacture of the adapter and they are sending another adapter out. They said its supposed to cure the blinking lights, which it did and the false light out which it did not. The trailer shop was reluctant about placing the resistors in the wiring as it would void the warranty on the Benz. They were thinking about placing them on the trailer but were afraid of something happening if I plugged into the Lexus as the load could tax that system and blow fuses.


Just another day of owning a Mercedes! PITA

farcohollis1369

If my 2011 ML 550 came with the towing option, is the trailer wiring plug in included?