The engine wiring can degrade because the insulating material falls off leaving the bare wire exposed. This can cause many problems depending on which wires are exposed and what they touch.Google+
Car Problem Reports
Mercedes-Benz S420 Insulation Degrades on Engine Wiring Harness and Leaves Conductors Exposed
Mercedes-Benz S420 Problem
Average Mileage: 137,333 mi (100,000 mi - 165,000 mi)
Having many issues with car like the climate control, unexpected instrument cluster failure, slight overheating. because the wiring harness has degenerated in the engine compartment. I have been told that car can not be diagnosed with out the wiring harness being replaced first. I was also told that this would be just the beginning of the money pit to fix it. How many hours should I be charged on the replacement of the wiring harness?
Visitor, 1995 Mercedes-Benz S420, 100,000 mi
Took my car in to replace the starter and was told the insulation around the wiring was degraded and I should get a new wiring harness. It has not caused any problems yet but it is just a matter of time. Estimate was $1,100 to replace the harness.