With colored pins highlight the circuits that are involved. eg. wipers blue seat heater green etc.

The way MB designs circuits typically things are connected at terminals or relays. The location in the wiring that all the non working items intersect is the nexus (identified by tiny face of Whoopee Goldberg)

A typical MB wiring problem is, push the brake peddle and the horn honks. Color code and trace the wires and the problem is the climate control servo.

Rocketman