Never mind, I found it:
If you have a volt=ohm meter, you can check the voltage of the battery with the engine off.
Then start the engine, and recheck voltage. If voltage hasn't increased to about 13.5 to 14 volts, charging system needs to be checked.
You can check the the stator voltage by unplugging the connector that comes from the engine that connects to the regulator. Set you meter to AC volts, start engine and run at full speed, voltage should be about 20 volts AC. If it's not, then the stator is bad. If you have 20+ volts AC then stator is ok.
Voltage regulator/rectifier can be checked by reconnecting stator and running engine full speed and checking voltage at the orange wire and the yellow wires. You should have 13+ volts DC at each wire, if you do not, replace regulator/rectifier.