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 600SEL Insulation Degrades on Engine Wiring Harness and Leaves Conductors Exposed
Mercedes-Benz 600SEL Problem
Visitor, 1993 Mercedes-Benz 600SEL, 125,000 mi
My body harness and engine harness both are failing due to the poor quality of the wire insolation used by Mercedes-Benz.