Sorry if there has been a misunderstanding. Concerning the negative earth Wassell, it is not that the polarity of the field coil is reversed, rather that the way it operates is reversed. Instead of the low side being connected to earth and the regulator sourcing current into it, the high side is connected to the dynamo output and the low side is pulled to earth by the regulator to get current to flow through the field coil.
I tried my DVR2 back on the bike again and following advice from the manufacturer I cleaned the armature with methylated spirits (he said to do this even if it appeared pristine). Also, since I took the dynamo off the bike to do this, I gave the field coil saddle fixing screws a good whack with my impact driver. This seems to have fixed things (either or both actions), at least for the moment.
I charged my battery Friday night before going out on the bike. There was no sign of much charging, but, on my return I switched to full beam and got a discharge reading but when I throttled up the ammeter steadied at Zero so the dynamo must have been taking the load.
We shall see what happens over the next few weeks. I think it is a bit soon to be shouting victory!