When faced with an illuminated charge light diagnosis on most late-model vehicles, do not automatically assume the problem is inside the alternator and potentially unserviceable. The problem could be the pulley and belt drive system. Neglecting to test and diagnose the pulley can lead to unnecessary replacement.
Bench testing an alternator on a test stand should verify whether or not its output is within specifications. If the unit tests bad, your customer needs a replacement alternator. But if the unit tests good, the problem is something else such as a bad voltage regulator, PCM or wiring harness. Loose, corroded or damaged wiring terminals at the back of the alternator are common causes of charging problems.
ALTERNATOR PULLEY DIAGNOSTICS
ALTERNATOR BENCHTESTING
