BMW 12321350052 Voltage Regulator

Disconnect the lead from the battery negative terminal, then disconnect the leads from the top terminals of the voltage regulator located on the bulkhead within the engine compartment, ensuring to identify the leads for exact replacement to their original terminals. Unbolt the regulator and lift it far enough to disconnect the leads from its lower terminals. If the regulator unit is faulty, which can be tested by an auto-electrical company, renew it with one of the same type. Refitting is a reversal of removal.

If the ignition warning lamp remains illuminated when the engine is running and it is confirmed that the drivebelt is intact and correctly tensioned, stop the engine and disconnect the multi-pin plug from the bottom of the regulator unit. Using a piece of wire, bridge the blue and black cable pins of the plug, then start the engine and run it at approximately 1000 rpm. If the ignition warning lamp goes off immediately, the voltage regulator is defective; if the lamp remains on or glows dimly, the alternator is at fault. A faulty regulator should be replaced, while the alternator may only be overhauled to the extent of installing new brushes; otherwise, it should be repaired by a BMW agent or replaced with a new or reconditioned unit, as special tools and equipment are required, along with the delicate nature of the diodes in the alternator.