eeferber

Ok - here's the scenario...overview: trailer LED running lights only flash when vehicle lights turned on.

1. 2011 ML350 w/factory hitch - this is how I ordered it.
3. verified correct and working trailer wiring at the trailer manufacturer
4. vehicle rear fuse panel - don't have the schematic in from of me right now, but panel fuse #72 is assigned to trailer, but is empty - meaning no fuse/no wiring...period.
5. verified good fuses for the other 2 assigned to trailer
6. however, the panel plug assigned to heated rear seats does have fuse/wiring.
7. I do NOT have heated rear seats.
8. could this fuse/wiring been inadvertently wired to the trailer hitch running lights.
9. electrical plug on the hitch - pole for running lights reads only 3.4v - shouldn't this be a full 12v.
10. anyone know what how much voltage goes to heated rear seats?

any suggestions to further trouble shoot this?

marc hanna

You probably need a resistor kit for the LEDs. Someone posted around here somewhere that MB sells an OEM kit.

Penn

The MB OEM system uses a SAM (Signal Acquisition Module) to control the trailer lights, let the stability control know that a trailer is attached, switch off the rear parking sensors etc. Unfortunately the W164 SAM module was not designed to operate with LED's.

Mercedes sell a resistor pack which resolves the problem or alternatively you can add resistors to each of the circuits. Warning if using unpackaged resistors - the resistors get quite hot and are ideally attached to the trailer so that the trailer frame acts as a heat sink (not recommended for boat trailers)

eeferber

for the record, and to close out this thread...

I located the following @ etrailer.com:
part#C57003 - 7-Way Trailer Adapter for VW, Audi, and Porsche Towing Trailers with LED Lights

it's a simple pigtail connector that plugs in between the vehicle electrical connection and the trailer wiring. Good secure 7 way plugs on both ends. The trailer end of the pigtail has mounting bracket should you wish to make it a permanent installation. I 'm not going that far as I rarely use the trailer. When I do pull the trailer, I will just zip tie the pigtail so it's secure and won't flop around while traveling.

Fixed the running light problem on my '11 ML350.

flybd5

You will need a 7-pin to 4-pin adapter that is for LED lights on the trailer. I have both, a normal one and an LED one.