When the alternator is spinning try touching a screwdriver blade to the bearing cap on the rear of the alternator (if it has one, Mopar alternators are configured like this). Be cautious of hitting any wire terminals to ground, though.

If you get magnetism, the alternator is doing something (although you don't know how much output it has) but could still be a culprit. If there is no magnetism, though, the alt is not doing anything.

This tip is more of a first-strike diagnosis and is NOT the full story.