The part number for the fog lamp connector is 018-545-38-28. I hold one in my hand because I have the same problem as you do. I been told that MB is no longer supplying replacement for it. In stead they issued a fog lamp kit (dealers sells it for $28 + tax). I don't know how to connect it to the existing wire. I took the front underbody panel down but the fog lamp wire is hard to see (on the driver side) around AC radiator (I don't know what to call it - looks like a small radiator about 6" by 6").