The engine wiring harness on these cars will either have been replaced or will be replaced. Use the search function on the top right of page to get a reading on this. You need to unwrap the friction tape like covering to get to the wires, and if they are bad it is readily noticed.
If you are the first or second owner MB has been known to pick up the tab on both the harness and the head gasket. Go to the dealer and use your saddest face, you might get it all taken care of. Ed