Turn key on, don't start.
Take ferous metal object (screwdriver/wrench), place in front of alternator pulley if shroud will allow, or back of alt, but don't touch any wires.
If you have a strong magnetic pull the object to the alternator, that indicates the brushes, rotor, voltage reg., and wiring are working.
This usually indicates the rectifier (diodes etc) aren't working.
If no magnetic pull, the voltage regulator, brushes, wiring would be suspect.
This is an out in the field test to get an idea what to buy on the way home .
Proper diagnostics with guages is preferable .
