Forgot about the wiring harness...it was found to be the source of my 300E having the same problems as yours.

As far as being able to detect a bad harness just by looking at it, here's a thread you might want to check out:

http://www.peachparts.com/shopforum/showthread.php?threadid=23813&highlight=wiring+harness

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car