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With the car running, remove the negative battery cable. If the car dies, your alternator is not working. If it stays running, then its fine. Thats the simplest way I know of.
 

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Although the time tested method of removing the battery cable to check to see if the alternator is charging "works", please be aware that sparks and hydrogen gas from a battery charging do NOT mix well. :eek: The results can prove very painful and overall a volt meter is much safer.
 

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Safe AND simple. Attach a voltmeter to the battery. Remove the plug from the voltage regulator. Start the engine. Connect a jumper momentarily between the A+ and F terminals in the PLUG (no more than 10 seconds). While attached, voltage should be between 14-16 volts. If not, alternator is NG, if so, alternator is OK, check regulator.

BTW, while removing the battery cable may work okay on a vehicle with a mechanical (contact) regulator, chances are that the voltage spike created will fry an electronic or internal regulator or possibly damage the alternator.
 
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