The dynamo wouldn' t charge. It seemed the cutout didn' t work at all. Some searching showed one of the connections had burnt away.
Making a new connection made the cutout work, but then the voltage was too high. No matter what adjustments I made, there was no difference.
So I fitted a new regulator. This is the smaller model without the fuses, so I fitted a fusebox too. Not entirely original, but at least now I have more fuses for some added security.