I am looking for a way to check if my alternator is putting out the correct voltage to charge the battery. Is there a write up for this somewhere? and also
if I have to change the alternator out anybody BTDT?
An easy test to see if your alternator is putting out voltage is to get a voltmeter on the battery, with the engine not running.

The voltmeter will display battery voltage, it should be around 12.5 volts.

Leave the voltmeter connected and start the car.
If the Alternator is working it, should now show a voltage of around 14.5 to 15 volts.

If the voltage drops below the 12.5 volts, then the battery is being drained.
This would be a strong indication that your alternator is not working.

Ken Postma 86.5 928S Auto
- Get a good voltmeter/multimeter, and set it so that it will read voltages from 10 to 20 VDC.
- Hook the red/positive lead to the positive battery terminal
(preferred) or the jump start terminal under the hood (usually acceptable).
- Hook the black/negative lead to the negative battery terminal
(preferred) or the bolt that attaches the engine compartment cross-brace (usually acceptable).
- With the battery fully charged and the engine not running, you should read 12.2 - 12.5 VDC. A lower reading means that the battery is not fully charged, or the battery is faulty, or there is a faulty connection between the battery and the voltmeter lead.
- Crank the engine, and hold the engine speed at 1500 - 1800 RPM. You should read 13.6 - 14.2 VDC. Lower means that the belt is loose or worn, or the alternator is faulty, or there is a faulty connection in the alternator or battery wiring. Higher means that the voltage regulator in the alternator is faulty, or there is a faulty connection in the alternator or battery wiring. (The flat ribbed belt should be really, really tight!)

If the alternator appears to be faulty, my recommendation is always that you find a good local auto electric shop. Not a parts place, not a general repair garage, but a shop that specializes only in repairing/rebuilding alternators, generators and motors. Take the alternator off and take it to them. Let them test it, and then and rebuild it for you if necessary. Tell them that you want it to have the maximum possible output. Remember that you MUST disconnect the battery ground cable before disconnecting or removing the alternator.

Wally Plumley
928 Specialists