If you know some basics, you can check it out and at least know if the alternator is charging. Are you having trouble with the batt going dead and needing jump starts? Set meter to DC volts. If not an "auto-ranging" type, set to the 20V scale, since you are checking for about 12-14 volts. As far as needing a load tester to check current, You have several options for creating an electrical load on your alternator while the engine is running. Before starting your engine, just put leads across the batt and see what the resting voltage is, If you have all the doors shut and car has set for several hours at least, and your hood light is not on, your resting voltage should be around 12.6 for a good battery. Next, fire it up and check the volts at the batt again without putting any electrical load on the system. Voltage should be around 13.5 to 14.5 Next, starting turning on the electrical consumers (loads). One of the biggest ones is your heater/ac blower fan on high. Now see if your alternator is able to maintain at least 13-14 volts. If not, rev engine just a little and see if the additional rpms bring it up to the minimum voltage while under this load. Bigger charging systems may need more electrical load to really push the alternator during testing, so turn on a few other items like the high beams, etc. If you start getting sub-13 volt readings while under moderate loads, you may have something going on. On older alternators, the brushes wear and eventually need replaced. Check all grounds underhood, too. The rectifier (changes charging voltage to DC from AC) will sometimes have a diode go out, reducing the current and affecting the alternator's ability to maintain 13-14 volts while under load.. Also, alternators with built-in regulators are prone to failure when this hot running regulator finally gives up due to where it lives inside the heat producing alternator.
