BMW E30 battery draining when parked and alternator check
E30 battery drains when parked – how do I find the current leak?
Disconnect the battery negative terminal and connect a multimeter or a small lamp between the terminal and the cable. Pull the fuses out one at a time; when the current stops, the leak is in that fuse's circuit. Then inspect the devices on that circuit.
What typically drains the battery while the car is parked?
Typical culprits are the instrument cluster service lights that stay on with the power off, a radio wired to constant power, and a glovebox or tailgate light that stays on. A faulty battery can also discharge by itself if there is a short between the cells.
What is the correct charging voltage and what do alternator faults look like?
The charging voltage should be 13.8–14.3 V. If the alternator gives 18–25 V, the fault is in the voltage regulator. If the charge light does not come on, check the cluster bulb, because the alternator gets its excitation through the warning light. Also check the grounds.