1) Start Car and run at a normal idle.

2) Connect a Voltmeter Directly Across the battery Terminals.

3) Turn on Headlights to High Beam.

4) check the battery Voltage.
*** The Battery voltage Should read between about 13.8 to 14.2 volts. (Possibly up to 14.5 Volts.)

5) Increase motor speed to about 1500 RPM. The Alternator should now produce a battery voltage between 14.2 and 14.6
Volts.
*** If it is Lower than 14.2 volts, the Alternator probably has one or more Bad Diodes.

6) Now, Maintain the 1500 RPM and Turn off the Headlights. Run this test for One Full Minute.
"The Battery Voltage should NEVER Exceed about 14.8 Volts".
***If it Does, the Alternators Voltage Regulator is probably Faulty, OVER CHARGING the Battery.

 

If the alternator went out, your car shouldn't start again after it dies. The theory behind a dead alternator, is that you're using up power and not regenerating any. When this happens, you have weak spark and then NO spark. The car sputters to a stop, and at this point since you can barely get spark you're certaintly not going to be able to get the starter going.


If the above isn't happening, I doubt it's alternator related.