The alternator keeps the battery in a constant state of charge anytime the engine is running. If your lights are dimming or you hear excessive bearing noise around the alternator, chances are that it's time for a replacement.
SKF Grooved Ball Bearing - 47X17X14 This item fits the following BMW Chassis: E30 M3,E34 M5,E30,E34,E36 Fits BMW Engines including: M10,M20,M30,M42,S14,S38