Alright, so part of the reason I got my E290 was because I wanted to tow with it. I'm going to get the hitch modified so I can attach a 2" ball in place of the euro 50mm one however I need to make up an adapter for the wiring as well. Here is a picture of the plug socket that's on the car. Does anyone know the name of the connector? I need the name so I can order one and make an adapter for my trailer which uses the standard flat trailer connector.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

https://en.m.wikipedia.org/wiki/Trailer_Connector/ISO

Seems to be an ISO connector haven't a clue where to order it from though.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

It's a euro 13 pin setup.

On the back of my G-Class I have the 7 pin euro plug which I have an adapter for a 4-way flat. (Similar to this one...and I had to add a wire to make it work correctly)
Trailer Wiring Adapter: 7 Way Euro Round To Flat 4 Conversion Plug

There are 13 pin to 7 pin euro adapters available so in theory you could connect 3 units together to make it work (13 pin--->7 Pin-->adapter to 4 flat)

I don't know if anyone makes a 13 pin to 4 flat adapter but they may be out there.

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1982 300GD Carmine Red (DB3535) Cabriolet Parting Out
1990 300SEL Smoke Silver (Parting out)
1991 350SDL Blackberry Metallic (481)

"The thing is Bob, its not that I'm lazy...its that I just don't care."

Products - Sockets 13-pin 12 V with screw terminals - Erich Jaeger

http://en.erich-jaeger.de/products/main-catalogue/13-pin-12-v-trailer-connectors/plugs-13-pin-12-v

Ok, so after looking at the links above, a lot of goggling etc, I've decided not to go the route of an adapter. I could buy one premade for around $65 + shipping but that seems like a lot for such a simple thing. I also found a PDF of a guy that made his own, but that still requires buying a plug from Europe as no one in NA sells them. I was able to find the pinout however.

So I think what I'm going to do is just buy a power tailor light converter (like this one http://www.amazon.com/Hopkins-46255-Power-Taillight-Converter/dp/B000CMKG6O/ref=sr_1_1?ie=UTF8&qid=1336008165&sr=8-1) since there's already fused power running to the euro plug. I'll just splice in behind the euro plug somewhere, run my wired to the converter, and then mound a 4-flat connector on the tow bar somewhere.

Here's the PDF I found with all the pinouts http://allroadfaq.com/downloads/howto/How%20to%20Make%20a%20Hitch%20Wiring%20Adapter.pdf

I think this will be a better solution as I won't have to worry about loosing my adapter or other such issues.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

I'd just follow the wires from this plug then locate where the plug into the body harness and make a new harness from there. Or cut the Euro off and use solder / shrink tube to adapt the style you want.

That's what I plan to do

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold