E320 wagon trailer light wiring - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 07-29-2018, 12:18 AM

I put a trailer hitch on my '04 E320 wagon today (removed from the '07 that I sold to my brother). The hitch installed just fine, but the wiring for the trailer converter didn't go so well. It seems the wagon has different colors for the lights than the sedan does. I originally saw a youtube video from E-trailer, showing what color wires and where they go. However, the wires in the wagon are not the same colors. Anyone have any idea where I can find what color wires to tap into? A little searching only got me an English site that was installing a Euro style trailer connection.

jay_bob · #2 07-31-2018, 09:24 PM

I did some digging in Star Finder and apparently the 211 has a trailer control module (device N28/1) code name AAG. It connects to the CAN-B bus and derives all trailer light signals directly. The drawings refer to a 13 pin connector which I think is a Euro standard.

I don’t think you can directly tap the lamps on a 211. The lights all come from semiconductor switches in the rear SAM and if you tap another bulb across the rear taillight bulbs you will probably upset the voltage sensing or even damage the SAM.

My 2008 ML320 has a factory trailer hitch and it is equipped with the USA standard 7-pin plug. I know that it is smart enough to know there is something plugged in there. It affects the engine/transmission shifting profile and also it supervises the bulbs.

Of course back when this was all designed, LED trailer lights were not a thing, so the supervision circuits were designed around the load of a standard incandescent bulb. I tried pulling a trailer with a 4-pin connector and LED lights. A standard 4-7 pin converter will not work, the car kept complaining about failed trailer lights. I had to go to etrailer dot com and get a special 4-7 adapter with load resistors to fool the rear SAM so it would work right.

ROLLGUY · #3 07-31-2018, 10:26 PM

Quote:

Originally Posted by jay_bob

I did some digging in Star Finder and apparently the 211 has a trailer control module (device N28/1) code name AAG. It connects to the CAN-B bus and derives all trailer light signals directly. The drawings refer to a 13 pin connector which I think is a Euro standard.

I don’t think you can directly tap the lamps on a 211. The lights all come from semiconductor switches in the rear SAM and if you tap another bulb across the rear taillight bulbs you will probably upset the voltage sensing or even damage the SAM.

My 2008 ML320 has a factory trailer hitch and it is equipped with the USA standard 7-pin plug. I know that it is smart enough to know there is something plugged in there. It affects the engine/transmission shifting profile and also it supervises the bulbs.

Of course back when this was all designed, LED trailer lights were not a thing, so the supervision circuits were designed around the load of a standard incandescent bulb. I tried pulling a trailer with a 4-pin connector and LED lights. A standard 4-7 pin converter will not work, the car kept complaining about failed trailer lights. I had to go to etrailer dot com and get a special 4-7 adapter with load resistors to fool the rear SAM so it would work right.

I too did some digging the other day, and found a similar thing. I could probably order the 13 pin light connector from Euro ebay, but I would have to adapt that to the 4-pin system. It may also be quite expensive. I had to use my trailer, so I got desperate and sort-of figured it out. For some unknown reason, the wagon has a totally different system than the sedan. What I found was that the rear lights have only two circuits on each side. One circuit is for the turn signal, the other for the brake/running lights. Using my test light with the running lights on, the bulb is dim. When the brake is pressed, the light gets bright. I have LED lights on my trailer. The turn signals work as they should, but the lights are bright whenever the brake is pressed and/or when the lights are on. I thought about getting a non-contact powered light controller, but I think I would have the same problem. I also thought about hooking up a separate brake light switch, and powering it directly from the battery. This may be the only (or easiest) way to do it. I would also need to tap directly into one of the side marker lights for the running lights. The way it is hooked up now, I have not gotten any lamp out messages, or anything like that.......Rich

EDIT: I had a standard trailer light converter on the three other W211 sedans that I have had (the wagon is the fourth car to use the same hitch), and it worked flawlessly. I found, and hooked it up according to a Youtube video from etrailer specifically for a W211 sedan.

jay_bob · #4 08-01-2018, 07:12 AM

I saw the reference in Star Finder to the same bulb filament for tail and brake and thought I must be reading it wrong. Apparently they are using the trick of pulse width modulation on the light circuit. Basically you feed the bulb a square wave and vary the on/off ratio to control the brightness. If they have the PWM tuned for the response of an incandescent filament an LED will not change brightness very much.

pawoSD · #5 08-01-2018, 12:12 PM

You can also get lighting controllers that use a sensor clipped (non-invasively) over power wires to the actual light modules, then uses 12V from another source (like rear power outlet) to actually run the lights. Thats what we used on my dad's 2007 E350 wagon. No wire mods or modules or cutting required with that setup.

ROLLGUY · #6 08-01-2018, 12:41 PM

Quote:

Originally Posted by pawoSD

You can also get lighting controllers that use a sensor clipped (non-invasively) over power wires to the actual light modules, then uses 12V from another source (like rear power outlet) to actually run the lights. Thats what we used on my dad's 2007 E350 wagon. No wire mods or modules or cutting required with that setup.

From post #3: "I thought about getting a non-contact powered light controller, but I think I would have the same problem." I didn't know the exact term, but the kind that has current sensors that clip on the wire.

These are very expensive (over $100) from what I have found. If I did use one of these, how would I separate the tail from the brake? It would seem that if I turned on the car lights, the brake lights on the trailer would light up. I think either way I need to hook up separate brake and tail light circuits that are isolated from the cars wiring. I could use the standard hard wired and powered converter (around $40).