Unlike the motorcycles of the past, today's modern roadsters are almost totally reliant on a fully functional electrical source to power their numerous on-board systems. This leaves modern motorcyclists relying solely on their bike's charging system to replenish the battery's power supply and hoping that the remaining charge is sufficient to return home after a long ride. To the relief of many riders, a voltmeter can be easily installed on nearly any motorcycle, informing the rider of the battery's condition at any given moment.
Test the voltmeter before installing it by connecting its positive (+) wire to the battery, then touching the negative (-) wire to negative terminal. The voltmeter should indicate a voltage of 12.5 volts. Remove the voltmeter's wires from the battery.
Select a location for your voltmeter on your motorcycle. Fully faired motorcycles often present more choices, but you must choose wisely to avoid unnecessarily damaging the expensive bodywork.
Splice the positive (+) wire from the voltmeter into a switched circuit, such as the speedometer lighting wire. This will prevent the voltmeter from drawing power when the motorcycle is off.
Ground the voltmeter's negative (-) wire. You may run the negative (-) wire back to the battery or ground the meter by connecting it to a screw or bolt on the frame.
Turn the ignition switch to the "ON" position and take note of the voltmeter's reading. A properly charged battery should read at or around 12.5 volts. Start the motorcycle and check the voltmeter. If your motorcycle's charging system is operating properly, the meter should reflect a voltage of 13.8 to 14.5 volts.
Obtain a wiring diagram for your motorcycle before beginning. Wiring diagrams can be found in a service manual specific to your motorcycle. If you are connecting the voltmeter to a circuit that is used for lighting, it may display a lower voltage due to the power drawn from the lights. If you do not feel comfortable working with your motorcycle's electrical system, contact a qualified technician. Follow all instructions provided by the manufacturer.