Thanks for all the advice, looks like the way forward is new stator wires, relocate the rectifier, and use an new RR51 losing the battery charging light (which never came on anyway).
Assume this will work? Anyone know why this won't?
Worked for me. I Didn't figure out the stator wire issue until I was on my fifth regulator. Three were replaced under warrantee by Ducati. They had no interest in why they failed, so they just kept putting in a new one. I got serious when I had to pay for the next one.
Possible bad news: Make sure you get the replacement right. The frist ST's ('97) ran on a unique charging system (400W) from Ducati which only lasted a year before being re-designed (450W) - probably because it was pants.
Possible good news: Talk to Duccati UK. They may pay for free fitting of a new one as they know how bad the system was. I doubt there are many originals still running out there. I know this sounds far-fetched for such an old bike, but they paid for mine when the bike was 7 years old. At the same time, check that there are not any re-calls still outstanding on your bike (use the chassis number). There were 3 or 4 for these models and 2 of them were important.
Will check out the system with Moto Rapido and if its not a 400w proceed with the improvements/repairs as above, watch this space for an update of whether this works!