Voltage read between any two wires from stator where they connect into regulator/rectifier.
Disconnect the stator to reg/rec plug, place multimeter leads between any of the two terminals in stator end of plug and take readings. Change leads between wires until all three stator wires are read.
The bike will start with this connector disconnected, if battery otherwise in good order.
You may notice oil in the connector too, caused by "wicking" up from the stator housing.
Manual states readings at 4,000rpm should be between 85 to 120v.
If one or more combination shows lower than that range then suspected burnt out phase in stator.
Take off stator cover and inspect stator - burnt out phase (3 of them) will show as blackened, or at least the resin cracked/burnt. But check for any loose/broken wiring either in stator or where wires lead from it and out of housing.
Hope this helps.