I am having unexplainable problems with my 70 westy

The generator light did not go off intermittently a few months ago, and I
even bought new generator/dynamo brushes, then the problem cleared itself up
and for some reason has just reappeared.

I checked that the genertor is working by remobiving the fanbelt and
connectng the generator to the battery, it span round great even with the fan
on so I think it is OK. I replaced the regulatot with a new one and the
problem is still there!!  wot can the problem be!!!

by the way I blew up my radio by jump starting the flat bus with reverse
polarity. can this have caused a polarity problem in the generator?

sam