How to Hook Up a Voltmeter to a Battery

The voltmeter is the easiest gauge to install. The voltmeter displays the amount of charge directed back to the battery. It can also indicate a battery with a bad cell and the operation of the voltage regulator. For instance, if the engine is running and the gauge is indicating 14.5 volts, and drops to 12 volts or lower when the air conditioner is turned on, that indicates a bad voltage regulator. If the gauge only shows 12 volts or lower with the engine running, the alternator is bad. If the voltage is 14 volts or higher with the engine running and the gauge shows less than 12 volts when attempting to start the engine, the battery is bad.

Instructions

1

Remove the steering column cover with a Phillips screwdriver to expose the ignition switch in most late model cars. In the early domestic versions, the switch is located on the top lower half of the steering column.

2

Locate the run wire exiting the ignition switch. There is a main power wire, a run wire -- which supplies power to everything in the vehicle -- and an accessory wire, which supplies just the accessories but will not run the engine. There is always a starter wire. This is usually a yellow wire and has power only when the switch is in the "Start" position.

3

Touch the voltmeter's black lead to a good ground. Probe the wires exiting the ignition switch with the red lead. Turn the switch to the "Run" position and locate a wire with power. Turn the key off and recheck the wire for power. When you locate a wire is that has power only when the ignition is on and none when the key is off, this is the voltmeter power wire. There are only a few wires between the battery and accessories for an accurate assessment of DC voltage from the alternator. Hooking the new voltmeter directly to the battery will drain the battery. Placing it between an accessory will show a drop when the accessory is turned on due to the draw from the item. The further downstream the gauge is placed the more it will indicate the resistance in the wire.

4

Cut a length of wire to travel from the wire on the ignition switch to the voltmeter, plus a little slack. Strip the insulation off one end of the wire with the crimping tool. Install a ring terminal connector and crimp it. Install the ring terminal on the B+ terminal on the back of the voltmeter and tighten the nut with a small wrench.

5

Install a T-Tap connector over the wire on the ignition switch. Push the wire from the voltmeter into the connector. Pinch the T-Tap over the two wires and use the pliers to compress the metal blade down inside the connector where it will pierce the insulation on both wires. Flip the T-Tap cap over the metal blade and snap it in place.

6

Cut a piece of wire to reach from the negative terminal on the back of the voltmeter to a good ground on the dash. Strip both ends of the wire and install ring connectors on the ends. Crimp the ring connectors. Install one ring connector on the negative (-) terminal on the voltmeter and tighten the nut. Install the opposite end under a screw or bolt on the dash.

7

Cut a piece of wire to reach from the voltmeter to a courtesy light, or if none are easily accessible, to the headlight switch. Strip the insulation off one end of the wire and install a ring terminal and crimp it. Install this terminal on the center illumination terminal on the voltmeter and tighten the nut.

8

Gain access to the back of the headlight switch and probe the plug for a wire that has power only when the headlights are on. Use the red voltmeter lead to probe the wires as you did with the ignition switch. Place a T-Tap connector over this wire and insert the wire from the voltmeter. Once again, use the pliers to compress the blade down over the wires and flip the cap over the blade until it snaps in place. Now the gauge will light up when the headlights are turned on. Install any covers removed previously to expose these components.