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 S500 Insulation Degrades on Engine Wiring Harness and Leaves Conductors Exposed
Mercedes-Benz S500 Problem
Average Mileage: 128,208 mi (42,000 mi - 200,000 mi)
Visitor, 1994 Mercedes-Benz S500, 89,549 mi
my s500 sdn,starts good,when warms up idle starts to come down and it shots down,will not start,it will
backfire when i try to start.after 30 to40 min,it get chance to cool down,car starts up and it is okay.
till next cold start
Visitor, 1995 Mercedes-Benz S500, 200,000 mi
the heater never goes off even when the car is off and kills the battery the rear break lights don't work and the windshield wiper works when it wants
Visitor, 1995 Mercedes-Benz S500, 42,000 mi
Degraded cables are causing intermitent electrical failures.
Visitor, 1995 Mercedes-Benz S500, 93,000 mi
car won't start.
Visitor, 1995 Mercedes-Benz S500, 149,325 mi
insulation on engine wiring degraded. replaced with new updated harness
Visitor, 1995 Mercedes-Benz S500, 85,000 mi
check engine lite always on!