How to Wire an Alternator Gauge

by Russell Wood

When you have a vehicle with a lot of electrical demands, you want to keep an eye on how much power your alternator is putting out to the battery. The easy way to do that is to wire a gauge for your alternator, which is called an voltmeter. But to get the voltage coming out of the alternator, you really have to connect the voltmeter to the battery and therefore the ignition wiring in the vehicle, since that's what the alternator is feeding. This job should take about an hour with the correct tools.

Locate a spot on the dash to mount the voltmeter bracket. Most people screw it to the bottom of the dash in a place where it's not visible, but where you can easily grab a quick look to see what your voltage is.

Screw the voltmeter bracket into the dash using the drill and self-tapping screws.

Strip 1/4-inch of wire off the end of the black wire using the wire strippers. Then crimp a blue ring terminal onto the end of the wire using the wire crimpers.

Attach the black wire to the negative terminal on the back of the gauge using an open-end wrench.

Run the black wire to a solid chassis ground, using zip ties to secure the wire to the vehicle along the way. That is a piece of metal on the chassis or dashboard that can provide a ground signal for the gauge. Typically, you can find a bolt hole on the inner dashboard that you can bolt the line to.

Cut the black wire to length using the wire cutters, strip the end 1/4 inch using the wire strippers and crimp a blue ring terminal onto the end of the black wire. Bolt the line through the ring terminal into the ground point using the open-end wrench.

Strip 1/4 inch of wire off the end of the red wire using the wire strippers. Then crimp a blue ring terminal onto the end of the wire using the wire crimpers.

Attach the red wire to the positive terminal on the back of the gauge using an open-end wrench.

Probe the wires underneath the steering column using the 12-volt test light. You want to find a wire that turns on when the key turns to the "on" position, so probe the wire, turn the key to on and see if the light on the test light turns on. When it has, you've located an ignition wire.

Run the red wire from the gauge to the ignition wire, using zip ties to secure the wire along the way.

Cut the ignition wire on the column, and strip both sides of the cut 1/2 inch using the wire strippers. On one end, crimp a blue butt connector to the wire using the wire crimpers.

Cut the red wire to length, and strip 1/2 inch off the end of the wire using the wire strippers. Twist this exposed wire with the bare ignition wire from the column, and push the twisted-together combination into the other end of the blue butt connector. Crimp them together using the wire crimpers.

Turn the ignition key to the "on" position. At this point, the gauge should sweep and show you the voltage of the vehicle. If not, check your connections and redo if necessary.

Items you will need

About the Author

Russell Wood is a writer and photographer who attended Arizona State University. He has been building custom cars and trucks since 1994, including several cover vehicles. In 2000 Wood started a career as a writer, and since then he has dedicated his business to writing and photographing cars and trucks, as well as helping people learn more about how vehicles work.