Originally Posted by pdrayton

Thinking of putting a tow hitch on your Mercedes W123? Here's how I did it.

I've been looking for a tow hitch / tow bar setup for my 1984 300D for a while now. I got the hitch on yesterday and towed my almost 2000lb boat with it and nothing fell off, so that's a good start. It was a bit sluggish, but that is to be expected. I'm going to measure the tranny temperature after towing for a while and compare it to normal and see if there's any reason for concern.

I thought I'd share everything I learned so it's an easy road for someone who wants to add a tow bar to their baby.

Towing Specifications for Mercedes W123 300D 240D
First off, towing ratings / specifications for the mercedes W123 are 750KG (~1650lbs) unbraked, 1500KG (~3300lbs) braked, but only in Europe. Apparently if you use the same car in the USA you can't tow with it, according to Mercedes USA . There is some speculation as to why this is, but no-one really knows, at least not anyone I read from.

Tow Bar
After a lot of searching around, I found a towbar from Uhaul. It is made by Curt manufacturing curtmfg.com and is Uhaul part # 28033. This hitch is rated to tow up to 2000lbs and retails for $99.95 not including labor, so it's Class I -200lbs GVWR, 200lbs tongue weight. It attaches to the bumper and subframe. Takes 4 holes and about 30 minutes to put on, pretty easy actually. It's not a big Class II type hitch. I'll try get some photos up.

The wiring setup is easy, once you have it figured out! So here's it all figured out! First, you have to buy a 5 wire to 4 wire converter. It's a little plastic black box adapter available in a kit or by itself from Walmart or Advance Auto (probably other places, those are just the places I went to). Costs about $15 for the converter, or $23 for the kit, which you will need if you don't have any trailer wiring stuff. I had a connector left over that I used.

The wiring is actually very easy. The kit above comes with splicing stuff, so you don't have to cut any wires on your merc. All you have to do is take out the driver side plastic molding in the trunk - the interior plastic molding that covers the antenna electronics, etc. Once it is out, you can cut a stripe in the wiring that leads to the lights and access the wires that go to both sides of the rear lights. Then it is a simple process of matching the colors below to the colors of the merc wires. If you don't have an american merc, you might want to check the Haynes or Merc FSM for the correct colors, or use a multimeter to make sure you have the correct wires.


Towing wiring: Use 5 wire to 4 wire converter from walmart.
Wires: Black/White = Left
Black./Red = Stop light
Black/Green = Right
Gray/Black = Tail light

If there are any questions, or something I haven't covered, feel free to post.

Happy Towing