The battery lights are notoriously unreliable. My 124 completely wore out the brushes on the alternator without any hint of a problem until the battery went dead. The only time I saw the battery light go on was when it lit up with all the other dash idiot lights at startup, there wasn't even a faint glow when the engine was running. Give me a good gauge anyday vs. an idiot light.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold