Measure the voltage at the battery, engine off, should be around 12.5 to 13 Volts.
Start the engine and check again it MUST be higher, should be 13 to 15 Volts.
IF he voltage is low find the rectifier, they are generally in the blower housing and will have 3 wires hanging off them.
Two will be the same colour and the other will be red or purple.
The two same colour wires will be to stator output ad should read 26 to 36 Volts AC between them.
If so then the alternator is working properly.
The single wire should read more than the battery voltage.
If the rectifier is bolted to the plastic blower housing it must have a ground strap grounding the body.
Very common to find the strap broken.
If so make up 2 short wires & ground both mounting bolts.
