Like all modern motor vehicles, Harley-Davidson motorcycles are much more dependent upon their electrical charging systems. Electronic fuel injection systems with high pressure fuel pumps, audio, GPS Navigation and more powerful lights that are on whenever the motorcycle is operating, add significantly to electrical demands. Charging system failure can be more than an inconvenience, so it makes sense to take preventative measures. The Onboard Diagnostic Voltmeter attaches easily to the battery and can be quickly viewed to spot potential charging system and battery problems. Works on all 6 or 12 volt battery and charging systems in motorcycles and many other applications.