factory trailer hitch - electrical issue
Thread Starter
Member
Joined: May 2010
Posts: 205
Likes: 3
From: Denver / southern AZ
'11 ML350
factory trailer hitch - electrical issue
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?
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?
Last edited by eeferber; May 17, 2016 at 07:34 PM.
Senior Member
Joined: Sep 2005
Posts: 251
Likes: 36
From: Melbourne, Australia
GLE 350D GLC 250D, Previous vehicles W204, W164, W163, W210 & W202
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)
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)
Thread Starter
Member
Joined: May 2010
Posts: 205
Likes: 3
From: Denver / southern AZ
'11 ML350
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.
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.
Super Member
Joined: Jun 2014
Posts: 507
Likes: 25
From: Massachusetts
2014 Smart ForTwo Passion Cabrio
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?
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?
