One tip for troubleshooting problems with an alternator is to use a multi-meter to determine the voltage output at the alternator's battery terminal. Alternators typically have between 13 and 14.5 volts of power output, although output may vary under load. Replace an alternator that produces no charge. Another tip for troubleshooting problems is to check the vehicle's interior lights while the engine is running, as lights that dim often suggest an issue with the vehicle's alternator.
The alternator generates the power needed to meet a vehicle's electrical needs. Mechanical issues that negatively impact the power output of an alternator can cause erratic symptoms that range from varying light levels coming from the headlights or dashboard display. Speedometers and tachometers that simply stop working or begin operating erratically is another common issue that may indicate a problem.
Alternators that are suffering from severe problems are unable to keep the battery charged for any length of time. When troubleshooting an alternator, perform a quick visual check to ensure the alternator belt is not loose or missing. Excessive belt wear and belts in need of an adjustment can also cause problems with the vehicle's electrical systems. Alternators may make unusual growling or whining noises as they give out, which can aid in troubleshooting the problems.