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 S320 Insulation Degrades on Engine Wiring Harness and Leaves Conductors Exposed
Mercedes-Benz S320 Problem
Average Mileage: 98,500 mi (60,000 mi - 145,000 mi)
Visitor, 1996 Mercedes-Benz S320, 95,000 mi
Wiring insulation degrades and bare wires exposed leading to shorts in various electrical components
Caused melted wires and shorting of mirror and fuse box
Visitor, 1995 Mercedes-Benz S320, 100,000 mi
deteriorated wire insulation causing drivebavility issues replaced with new wire harnnes
Visitor, 1996 Mercedes-Benz S320, 80,000 mi
Engine cuts out while driving. Must be restarted.
Visitor, 1995 Mercedes-Benz S320, 60,000 mi
Running rough. Had to replace wiring harness.
Wiring harness decayed and needed replacement