You should take a look at various points on the harness. Look near the packs where the spark plugs are, look near the temp sensors. Open up the outer insulation and see if you see cracking/deterioration. If you do then time for new harness without question. This problem effected 124/140s from 92-95 or so. My 201 escaped this problem.
PeachPartsWiki: W124 Engine Wiring Harness Replacement
The part number for the harness is
That PVC tape job is the ****tiest job I've seen. I had a squirrel or something chew though my passenger headlamp/running lamp wire up near my battery once.
My buddy bought a 93-300E and it needed a head gasket done. My mech wouldn't touch it without the harness being replaced (the harness was infact bad). Once you start moving those bad harness around theres no telling what damage will be done.
The harness is about $750 new on XXXX
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