A voltmeter allows you to keep track of the amount of electricity flowing through your boat's electrical system. If your boat's entire DC electrical system operates at the same voltage, whether it is 12VDC, 24VDC or 48VDC, you can install the voltmeter anywhere in the boat's electrical system. Mixed systems -- part of the electrical system is 12VDC and part is 48VDC -- require a voltmeter for each system. A voltmeter on the boat's dash lets you track the boat battery's performance.
Inspect the under-dash area where you wish to mount the voltmeter, to ensure no wires will be damaged when you cut the hole for the instrument. If wires can be pushed out of the way, hold them back with duct tape.
Cut a hole the size of the body of the voltmeter in the boat's dash, using a hole saw. Sand the edges of the hole with sandpaper to smooth the voltmeter's entry into the dashboard.
Crimp spade terminals onto the wires of the voltmeter, using a wire crimper. The voltmeter has three wires coming from it, the red power lead, the black ground wire and the white wire that provides power to the voltmeter's instrument light.
Loosen the screw of the power terminal of the instrument next to the voltmeter. Push the spade terminal of the red wire under the screw and tighten the screw with the screwdriver.
Connect the white wire to the light terminal of the instrument adjacent to the voltmeter. This is the wire for the voltmeter's light.
Unscrew the ground terminal screw on the nearest instrument. Connect the spade terminal to the ground terminal of the adjacent instrument and tighten the screw.
Turn the key switch to the "On" position. A fully charged battery shows between 12 VDC and 14.4 VDC for a fully charged lead-acid battery. If your boat use a gel-cell battery, the voltmeter will show between 12 VDC and 14.2 VDC.
- Disconnect the negative cable of your battery before performing any maintenance work on your outboard motor to prevent electrical shock or accidental starting. Remove the nut from the negative post with a 5/16-inch box-end wrench. Lift the cable from your battery, move it outside of the battery box and close the lid of the battery box. After the work is complete, reconnect the negative battery cable.