The alternator is an indispensable piece of any vehicle's electrical system. If it malfunctions in any way or fails completely, the battery inevitably discharges to the point where it is no longer useful. This is due to the fact that as the engine runs, it turns a belt which powers the alternator. The alternator then generates an electrical charge that is distributed to the battery, as well as other electrically-powered accessories on the vehicle. If the alternator is not working, an inadequate supply of electricity will result and the battery will die.
Open the vehicle's hood and find the alternator within the engine compartment. The precise location will vary depending on the make/model of the vehicle. Regardless of its location, the alternator will utilize a pulley and belt.
Inspect the belt after you've found the alternator. The alternator's belt must be tight. If it's loose, it will not run the alternator properly. This will result in poor electrical output. Also, if the belt is damaged, cracked or worn, you should have it replaced.
Inspect the mounting brackets and bolts that attach the alternator to the engine. The alternator must be secure. If it is missing any bolts or is loose on the mounting bracket, it will not function correctly. Replace or tighten the bolts as necessary.
Ensure your hands and all tools are away from any of the vehicle's moving parts and have a helper start the engine. While the engine is running, listen specifically to the alternator. If you hear any grinding, the alternator most likely has worn or broken bearings, or a bad diode. A screeching sound is more indicative of a worn out or loose belt.
Turn the vehicle off for a moment while you attach a digital voltmeter to the vehicle's battery. Be sure to connect the voltmeter properly and securely. The voltmeter's positive and negative clamps or leads must be joined with the matching positive and negative terminals of the battery.
Ensure all tools, wires and body parts are away from any moving components of the engine and have your helper start the engine once again. The voltage reading that appears on the voltmeter should fall into the 13.8 to 15.3 range, or approximately 1.5 to 2 volts greater than the actual battery voltage, which is usually 12 volts for most cars and trucks. A reading that is too high or low could indicate anything from a defective regulator, improper grounding, corroded terminals or shorted/bad diodes.
