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 300CE Insulation Degrades on Engine Wiring Harness and Leaves Conductors Exposed
Mercedes-Benz 300CE Problem
Average Mileage: 120,625 mi (94,500 mi - 171,000 mi)
Visitor, 1992 Mercedes-Benz 300CE, 94,500 mi
engine shutts off, and takes a while to restart..
unable to fix, many mechanics have tried to fix, to no avail..
Oil pressure light started going crazy after a routine oil change. Then the low oil light came on. After diagnostics took place, the wiring harness to the oil sensor and oil pressure guage was bare, shorting and causing the problem. That particular harness was replaced. I still haven't replaced the other harnesses.
Visitor, 1991 Mercedes-Benz 300CE, 171,000 mi
Began with shorted Clock which drained the battery. Evolved into Fuel Distributor issues causing Misfires, poor idle, Lack of pick up and stalling.
valve cover gasket leak and head gasket,engine harness degraded