How to Test the Nodes in an Alternator
A car's alternator is the main power source for electrically powered mechanisms and devices. While the battery provides the initial power to start the engine, the alternator provides constant power to the radio, air conditioner, lights, power windows, automatic closing doors and the trunk. Often times, when a car does not turn over and there is little or no power to the interior lighting, the first failing component to consider is the battery. But if the battery is good, the alternator has to be tested.
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Instructions
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Turn the car off and lift the hood. Check the alternator belt first to see if it is loose before performing any other checks. Even if the alternator is good, the belt must be taut in order for the alternator to provide current.
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Leave the engine off on use a Voltmeter to check the battery first. This is necessary to determine the actual source of the problem. Place the Voltmeter's red lead on the positive pole-stud on the battery and the black lead on the negative pole-stud on the battery. The Voltmeter should read between 12.5 volts and 12.8 volts.
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Check the alternator's output to see if the alternator nodes are functioning properly. Turn the engine on and let the car idle. Place it in "Park" and apply the parking break as a safety precaution. Place the Voltmeter's red lead on the battery's positive pole-stud and the black lead on the battery's negative poles-stud. Look for a voltage output reading of 13.6 volts to 14.3 volts.
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Tips & Warnings
Two other methods for checking an alternator are to start the engine and remove the positive lead to the battery. If the car's engine shuts off, the alternator is probably bad. The second method is to place a screwdriver near the casing on the back of the alternator to feel for a magnetic pull. No magnetic pull means the alternator is not properly working.
References
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