2003 ML350 - I need the trailer hitch 7-wire connector plug, the plug into which the trailer wiring plugs. The MB installed plug is broken and MB no longer supplies parts for the factory installed hitch. The factory unit is a standard circular 7-wire plug to the trailer and the connection to the factory wiring harness is a rectangular plug. Can only find after market plugs requiring me to cut off the factory rectangular wiring harness plug and connect loose wires into the after market connector.

 

I believe the wire harness assembly is Q6 54 0013 , very hard to find item. Ones in a while there is used one on e-bay for about $150. Many people who bought aftermarket hitch are in search for this part. What is wrong with your original if it is not repairable?
I got very lucky and found new oem ORIS set for $200
Use shrink wrap tubing, solder each wire to wire for trouble free installation. Good luck.