I have 1944 BSA WM20, is there some simple way of identifying the polarity of the bike and magdyno?
i need Positive/earth or negative/earth regulator?

thanks

You decide what you want either positive or negative. Say for arguments sake you decide on negative for easy access to LED bulbs. Buy your negative earth electronic regulator, wire your battery for negative earth. Take the field wire from the dynamo and flash against the positive battery terminal this will polarise the dynamo for negative earth operation. Then attach regulator. If positive earth reverse the procedure.

I second Ian's opinion. Go negative earth. The bike would have been negative earth originally.

If you buy a negative earth DVR2 regulator, then you can run either 6 or 12 volt electrics (read the instructions though!).

Personally, I would run a 12v system on LEDs; at least people can see you!

email (option): sacombsashtrees@hotmail.com