Are you in a position to disconnect the 4 wires and put an AC voltmeter between the violet wires, rev the engine and tell me the voltage you get and then do the same with the other pair of wires. I have read somewhere that this should exceed 50 volts AC but Hitchcocks say 30 volts. Of course, once you reconnect the wires that voltage will be less due to the load of the rectifier/regulator and the AC regulator even with the headlight off.
Alas, I'm not using that alternator anymore--I have an aftermarket two-wire resin encapsulated job, and the old one is either discarded or in storage in the States. Sorry I can't assist.