Body Electrical, Comfort and Convenience Systems
Systems to know
These are the circuits drivers notice first: wipers and washers, power windows, central locking and keyless entry, instrument clusters, horns, mirrors, seats, sunroof and blower motor. Most are now driven by a body control module over a data bus, with local smart motors.
Wipers. A permanent live plus a park switch lets the motor return to rest after the switch is released. Faults include no park, no intermittent, incorrect sweep from a mis-set linkage, or a rain sensor needing recalibration. Windows. Many systems measure motor current to detect obstruction (anti-trap) and use one-touch control, so they need normalisation/calibration after battery disconnection or motor replacement. Locks. Actuators are usually two-wire reverse-polarity motors or small solenoids; a single dead door is often an actuator or a broken wire in the door loom bellows. Instruments. Clusters receive data over CAN; a dead gauge with live data often means the cluster, not the sender. Horn. Usually a relay and a horn behind the bumper, with the switch earthed through the clock spring - a horn fault alongside an airbag light points at the clock spring.
Traps
Condemning a motor before checking supply and earth under load; forgetting normalisation after a battery disconnect; mistaking an anti-trap trigger for a failed regulator; assuming a central-locking fault is the fob when one door works; and treating a warning lamp as a cluster fault when the module is reporting a real condition.
Rule of thumb. Load-test both the feed and the earth at the actuator with a bulb or test load. If the lamp lights brightly on both, the fault is in the motor or its mechanical drive - not the wiring or the module.