Unplug regulator. blue and earth = 26 - 30 vac @ 3000 rpm.

Unplug stator. red to white = 90 -140 ohms. green to white = 800 -1100 ohms.

Insert an ammeter betwen red wire and battery +. With engine @ 3000 rpm and battery @ 13 vdc the ammeter should read 1.5 - 2 amps

un-plug the regulator and check that you have battery voltage on the red / white wire that plugs into terminal "C". The regulator needs this input to function correctly.

Check for good earthing between engine and chassis / battery / regulator.