How to Test Voltage at Alternator with multimeter ?

Nov 09, 2003 3 Replies
U

Hi,



I have an 88 GTA 5.7 I have a low voltage condition, meaning the car runs at about 9 or 10 volts now, and is going down slowly. Started reading lower and lower a few days ago. I think I must be running totally off the battery, although the battery tests currently at 11 volts ( even though the dash guage says 9 or 10). Soo, where do I touch hook up my voltmeter pos and neg pins to the alt to test it with the car running ? I have the 3 pin connector. There are 4 holes in the connector, but only 3 pins in it. The wires are red, yellow, and brown.



I think the dash guage is right, as far as the volts being low, since the wipers have gotten slow since the readings have dropped.



I'll probably take the alt out, to autozone to test it, eventually, but I'd like to test whatever I can myself first.


Thanks


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J

The thick red wire. It's almost certainly the alt. Most parts stores can test it for you.

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B

Start the car. Rev it up and keep it at 2000 rpm or so (you may have to have help) measure the voltage across the battery. It should be 13.5 to 14.5 volts DC or so. If its not, the alternator is not putting out. You may have a battery problem too. If you pull them to check, get both tested. You have cleaned your battery posts?

BOB

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U

Yes, have cleaned posts. Battery tested at low amps (52) , but the machine at Autozone did not specify the volts (weird). My voltmeter said 11 volts on the batt, car off.

Had alt tested at 2 parts stores. Both said the alt was only putting out 1.9 volts !

Am installing a new alt soon.

Thanks

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