Be sure to use a resistor with a high enough wattage rating. At full output the alternator will produce 120 watts. I've used a 10 watt, 1 ohm resistor with no problem. I think I got the 10 watt resistor at Radio Schack. Hook everything up, resistor and meter, then start the engine. Once you get the reading, shut it down. Continual running will burn up the resistor.