Hi,
Tom,
I would have the rectifier regulators checked by an auto electrical workshop, they have bench setups that will check its performance
Check for an earth fault on the bikes alternator, I remember finding this fault and being told it was common at the time ( c1990-95 ??)
An earth fault would play havoc with the bike, including blown bulbs etc. does the headlamp flicker at low revs??
If my reasoning is correct a diode could be put in series with one leg of the alternator output
reducing the output by half
I have never tried this on a bike but have done it on a welder !!!
John