How do you test a cars alternator?

Answer 1

1st you start up the car. Hook up a voltmeter to the battery, and put a load on the battery as the car is running (have the lights on, radio on, high beam on,...) after you put a load on the battery read the voltmeter. if it goes below 12 the alternator is bad. It souldn't be no more than 14 volts. you can also use the battery gauge but to be 100% sure hook voltmeter to the alternator.