I see from your images that your parts are the same as the ones I had from a euro 108 trailer hitch. I still have the 6-pin pass through plugs. Makes hitch wiring nice, independent of whether or not you have a european hitch. (Or more correctly, a non-US hitch). It still doesn't make the system plug-and-play with a euro hitch since technically US hitches are required to have a chain connection in addition to the ball/socket connection. Euro hitches don't provide for a chain so technically they aren't legal in the US. If you really want to nit-pick, the ball is also a slightly different size, but close enough. If you want to read about it, go to wikipedia and look up trailer hitch.

If you are going to add a hitch to your Mercedes and IF you have tail lights that plug into 6-prong sockets like these, it's really nice to have the pass through sockets even if you don't use the outlet portion. By the way, I think that the outlet portion is supposed to have more of a bracket on it that connects to the undersideof the car / hitch / bumper / something. From the picture it looks like that rusted off.