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Ampmeters (ammeters) versus Voltmeters.
For BMW Airhead motorcycles.
Explanations & Problems.
Relative merits of ammeter vs. voltmeter. Use both?
Voltmeter reading problems with the stock... or aftermarket... voltmeters?
Why not just a GEN light?

© Copyright, 2014, R. Fleischer
http://bmwmotorcycletech.info/amp&voltmeters.htm
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SUMMARY:
I see little reason in having having an ammeter permanently installed on any BMW motorcycle, unless you have special circumstances. I foresee several drawbacks, not the least of which is a potential fire hazard, which includes burning up your bike's wiring; besides the usual situation of LESS reliability with many modifications; especially with added electrical items.  I will lay out the benefits, and the problems, for both ammeters and voltmeters. The GEN lamp provides quite a bit of information if you interpret it correctly....but it may not be enough FOR YOU.

The GEN lamp, voltmeters, and ammeters:
The GEN lamp has several functions. It provides an illumination to instantly see if the alternator is likely to be producing electricity.  It may also provide information if the alternator is intermittent with RPM or brush wear, or diode board problems. It might indicate, by a DIM indication, of problems with connections.  It does not indicate the level of charging or discharging; and, it is a very broad type of indication, indicating an operating charging system...or not. It is reasonably decent at doing this, and cheap for a manufacturer to include. Long ago, alternator-equipped cars were mostly equipped with such lamps, and not ammeters nor voltmeters. Many cars still have GEN or ALT function lamps, & do not have voltmeters, although many modern cars have voltmeters built-into their in-dash electronics displays. In the same way that cars that do not have manual shift gearboxes but are equipped with mechanically and electronically controlled automatic transmissions do not need tachometers, so it was with alternators and voltmeters and the charging lamps. Lamp ON, ....there is a gross failure. Lamp intermittently ON.....there is a gross failure coming soon. Simplified descriptions, but fairly accurate. 

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