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the only reliable way of determing if your alternator has gone bad is to have it tested by an automotive electricial specialist. That is because most modern alternators have the voltage regulator built in, so just testing to see if it is generating will not tell the whole story. Warning signs of alternator/voltage regulator failure are dead battery, but battery can be charged, lights dimming and getting brighter while driving, and hard starting.

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โˆ™ 2007-06-22 17:33:56
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Q: How do you know if your alternator on your 91' Geo Prizm is bad?
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How do you know if your alternator is bad?

If it is makeing a noise or is not putting out at least 13.5 volts it is bad. Take the car or the alternator to an Auto Parts store and have them load test the alternator to be sure.

How do you know when alternator is bad?

Typically you know your alternator is out when you have to jump start your car numerous times. A way you can test it is by turning on your car and while it's running discount the + terminal. If the car turns off then your alternator is bad. If the car remains in then alternator is good and possible bad battery. Hope this helps

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