Amp Light stays on.

Just turned my car on and the alt light stayed on. Dash reads 8 Volts.

How can I make sure the alternator is indeed defective.

Don't want to replace something which is not defective.

Can you take it to an Autozone, advance auto, or O'rilley's? They'll usually check them for free or a couple of bucks. Also, make sure all of the wires connecting to your alternator are tight. I had one come loose on a car once (91 Tempo) and it caused the light to stay on even though it was charging fine.