A voltmeter is a great accessory that will help you determine how well your car's battery and alternator are working. The voltmeter will be able to tell you how the alternator is operating in conjunction with keeping the battery charged. Keeping an eye on the voltmeter in your car will tell you whether or not the alternator is bad. When the alternator is good the battery will remain at a constant 12V rating. The opposite also means that the alternator is bad. If the voltmeter shows that the volts is up to around 16 or more, it means that the alternator is not regulating the power well and needs to be replaced. Here are the steps to take to wire a voltmeter for your car.
Step 1 - Determine Voltmeter Location
Your voltmeter should be located in a place where you can see it easily without having to take your eyes too far away from the road. Above the dash, on the left-hand side, near the corner of the windshield is a good place. Of course, you can place the voltmeter under the dashboard on the right-hand side as well.
Step 2 - Attach Voltmeter
The voltmeter will have a small mounting bracket that needs to be attached in order to mount the voltmeter. This simply attaches with the supplied screws. Once the bracket is secured you can then place the voltmeter in the bracket.
Step 3 - Connect Wire to Voltmeter
There are two connections at the back of the voltmeter where you will make your connections. Use the 16 gauge wire and strip back the end of the wire. Make sure you place the correct wire on the positive and negative poles on the voltmeter.
Step 4 - Locate Wire Harness
Remove the bottom of the dashboard and look for where the wire harness is. You should see a bundle of wires coming from out of the firewall near the steering column. Probe these wires with a multimeter to find a wire that has power to it without the key being turned on. These wires will usually have the same colors, but some manufacturers are different.
Step 5 - Connect Ground
Take the negative wire from the voltmeter and make a good connection on a grounded screw in the car.
Step 6 - Connect Positive Wire
Use one of the wires that you found in the wiring harness and cut it between the steering column and connector in the dash. Connect the end coming from the steering column to the voltmeter. Take the piece of 16 gauge wire and complete the circuit by connecting it to the connector wire. Use a wire nut to make the connection.
Step 7- Test Connections
Once you have all of the wires connected with the power and voltmeter, you will need to test it to make sure everything works correctly. Turn the key on and see if the voltmeter registers a reading. If it shows that the battery is discharging after you start the car, you have the wires configured wrong. Switch the positive and negative wires.