What an alternator actually does
An alternator is a pulley-driven generator. Rotor makes AC in the stator. Diodes turn that into DC. A regulator holds about 13.5–14.5 V.
The alternator is not a battery. Start at the pulley. A ribbed belt from the crank — serpentine, or an older accessory belt — lands in those grooves and turns the shaft. The engine is what spins it. This case just has to follow.
Inside, a rotor turns in a stator. That is AC. Brushes ride slip rings and feed the field so the rotor is a magnet. No field, no charge — even if the pulley is screaming. The little board that holds those brushes is the regulator. It is not a fuse. It is the part that decides how hard the field gets fed.
A diode bridge in the rear case turns that AC into DC. What leaves the B+ stud is the feed for the battery and the loads. The regulator holds the system around 13.5 to 14.5 volts so the battery charges and the lamps stay bright. Weep dust, a growl, lights that sag at idle — this unit is dying. Do not start at the battery.
