I agree that you should change the wire harness for sure, but have you tried to reset adaptation for the computer just to see if you can get the car going again?

After you've cleared all the codes out and are only getting a single flash after pushing the button, hold the button down for 6-8 seconds 2 seconds after you see the single flash, turn the key off for 2 seconds, then on for 10 seconds and then start the engine.

I don't know if this will help but I don't think it can hurt either.

__________________
1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles