Ammeters, Voltmeters (and Ign Telltale)

To inform the driver of malfunctions in the charging circuit, modern vehicles have only an Ign. warning light. This is inadequate for the more informed driver. The two instruments available (usually as a retrofit) to the driver (not service technician) is the ammeter and the voltmeter. So a few questions. How does the Ign. warning light work? What can we learn from it? How do we interpret it? How do we interpret the results of the ammeter. And the voltmeter. Why did older cars have an ammeter, and newer cars a voltmeter? If we want to retrofit one in our vehicle, how do we go about doing it. Any special points one needs to be aware of? If we have to choose between ammeter and voltmeter, which one should we choose and why? Hoping to have an informed discussion (and no useless internet links!) Regards Sutripta

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