Repair wire harness for Air Mass Meters is 140 440 76 37. About $100. It has two connectors and long wires with pins. It comes with instruction and special tool for extracting old pins from the connectors. Installation requires taking apart computer box, removing old wires from the bottom connectors and replacing them with new. It took me a few hours to install.
The main engine harness p/n 140 540 47 05. Very easy to install. It is on the top of the engine and goes to all 12 injectors and a few sensors at the front. It was around $400. These p/n are for 92 600SEL, make sure they are good for 93 MY. AFAIK
, throttle actuators wiring harnesses are problematic too, but I don't think you can get just the harness, have to replace the actuators. Big $$$. If yours are bad, maybe try to repair or replace wires separately.
I can't see how the throttle actuator can cause running rich. It just gives air to the engine. Then it is a job of the Air Flow Meter to measure it and send the reading to the computer, and computer responds with the proper command to the injectors so the fuel can be matched up to the air measured.