Hi, I don't know anything about G, but I just did a ML hitch install a couple of weeks back. I would like to report some information about the installation, to see if it would be helpful.

The kit I ordered has a special template for cutting MY02 bumper, so I assume it is the most recent kit from MBUSA. The kit comes with a 4-head harness. 3 heads are at the vehicle side, 2 of them are plugged into a black plastic box, with a piece of PCB in it and I remember something like "trailer brake control" I read somewhere about it. The other one on the vehicle side plugs into the vehicle wiring. The trailer side is a 7-pin round (excuse me here, I am completely new to the trailer stuff, installed hitch for my bike rack) connector/socket. The kit also comes with a 7->4 connector. It looks like standard trailer hook-up, based on my limited Walmart observation. The 4-pin plug can plug into the 7-pin socket.

BTW, for anyone who try to connect the harness, do NOT follow MB's instruction to locate the vehicle side connector from inside the cargo area. After remove two plastic covers, I just couldn't find the pre-wired hook-up. I finally found it after removing one of the two body vents cover. It is very easy to access the pre-wired connector there.