This is the 3rd alt I put into my car. I took it back and they tested it, said it was working. But in my car it reads 8v.

Can there be an electrical problem elsewhere draining all the power?

 

Slow,

If you are using the dash-mounted voltmeter to analyze the problem, you shouldn't. Use a separate handheld meter to check the alternator's output voltage at the stud on the back of the unit.

 

i was using a voltmeter

 

If you're using a separate (calibrated) meter, you should check for belt slippage, low RPM (underdrive sheaves or low idle), poor ground connections, failing field connector, or a shorted cell in the battery.

Try disconnecting the battery after it is running to see if the voltage increases.

Test maximum output by grounding the test tab through the hole in the rear alternator case:



Do this only long enough to get a voltage reading. You should be able to produce 17-18 VDC or more. If so, the alternator is O.K.

Test teh voltage at the field connector with the ignition on and engine off. Onc of the terminals should have battery voltage.