7 Pin Towing Plug Wiring. Verify the harness color codes at each tail light. The length of copper to expose may differ depending upon your replacement plug.
One thing I assuming is that MB wires all of those pins to work on their factory installed towing system. The three additional pins are: trailer brakes, back-up lights and trailer battery charging. Hopkins trailer plug / adapter prevent the need to rewire a vehicle or trailer when the connector styles do not match.
There should be a common color for both the tail lights.
Jim, does your trailer just use the standard plug?
You were looking for the wiring diagram/colors for the truck connectors instead of the trailer plug wiring. My left fuse box lid says, "Trailer Harness fuse located below RH side of glove box near kick pane. Use your wire strippers to remove the shielding from each wire.