Mercedes-Benz W140 crumbling engine wiring harness insulation
Why does the engine wiring harness insulation crumble on the W140?
In an early-1990s Mercedes, the wire insulation is biodegradable and cannot withstand heat. Near the engine the insulation turns brittle and crumbles, leaving the wires bare. The problem affects at least the M104 and M119 engines.
What symptoms does a worn W140 wiring harness cause?
The harness carries engine data to the tachometer, glow plugs, temperature gauge, cruise control and oil pressure, among others. Symptoms can include weak acceleration, a cruise control that does not work and sensor faults. The sensor wires running close to the engine are the most at risk.
How is a crumbled wiring harness repaired?
The harness can be replaced completely, or the wires can be repaired by soldering them to the old connectors and protecting them with heat-shrink tubing. The engine harness part number is A1405402005, but the original part is no longer manufactured. Replacing the harness is about three hours of work at a workshop.