Early-90s W124s left the factory with 'eco' harnesses whose insulation embrittles and crumbles with age, making harness replacement one of the first questions every buyer asks. The accepted fix is an updated, VIN-specific non-biodegradable Delphi harness, though some argue any car still running after 30 years has almost certainly already had it done.
Biodegradable engine wiring harness
Mercedes-Benz W124 E-Class · mechanical