If you have a multimeter, you can use that instead. A multimeter measures voltage as well as other electrical properties such as current and resistance. You want to measure voltage when you’re checking your alternator. [2] X Research source
Turn off the car. You’ll want to make sure your engine is off before attaching the voltmeter. [4] X Research source Open the hood. Connect the voltmeter to the battery. Place the red lead of the voltmeter to the positive battery terminal and the black lead to the negative terminal. Avoid touching your skin to the battery. Read the voltmeter. If the battery reads above 12. 2 volts, it has enough juice to start the alternator, which can then be tested with the voltmeter. If the battery doesn’t have enough voltage, either get the battery charged and re-test or try a different method for checking the alternator.
Repeat the process with the lights, radio, and AC on. The alternator is charging if the battery voltage stays above 13 volts with the engine at 2,000 rpm and all accessories on.
