Make sure that you use the correct voltage setting too, unless it's auto ranging. You'll want to select the one that reads DC voltage (which on the meter is a solid line with dotted line below it) and select the right range (which will be the volts in ones). Most meters will let you read millivolts, thousands of millivolts (or just volts), tens of volts, and hundreds of volts in DC. Make sure also that you don't put the meter in between the wire and the alternator because you will get a wrong reading, just leave it hooked up and put it on the terminals.