Power is supplied to a vehicle's engine ignition, electric door locks, alarm systems and other accessories by the 12-volt circuitry that runs throughout the vehicle. When a circuit fails, you will find that a 12-volt tester is an invaluable tool for locating the source of the problem. If you are a do-it-yourself auto mechanic who understands basic electrical circuits, you can verify the presence or the absence of electrical power in your vehicle quickly and confidently by using a 12-volt circuit tester.
