I'm not seeing the picture. If you remove the switch, which will not likely be used with an electronic regulator, how many wires come out of the alternator coils? I would guess four, one from the common connection, and three more from the ends of the three coils. Is that correct?
No not quite. There are three stationary coils and six permanent magnets on the flywheel alternating in polarity i.e. N -S - N - S - N - S The coils are mounted at 120° to each other in a triangle arrangement. The magnets are spaced such that each coil is excited at the same time by a pair of magnets as the flywheel rotates which I guess makes it a single phase alternator (Lucas used to make a three phase alternator).
The connections are one terminal post with a common connection to one leg of each of the three coils and two other terminal posts. Of those two terminals one has connection from the remaining leg of one coil and the other has a connection from the remaining leg of the remaining two coils. The 8 pole switch, at the same time as selecting ignition, ignition and pilot lights or ignition and headlight also switches the alternator coils bringing into circuit one, two or three coils as required. To put it another way one coil is connected alone, two are connected in parallel and all three have one common leg. I hope that makes sense!
Regarding converting the bike to 12V. The reason I am reluctant to do so is that the owner's club had a very knowledgeable adviser on all matteers related to old fashioned vehicle electrical systems. He wrote many articles for the club magazine and his background was in this area. I was in correspondence with him when he recently, sadly, died quite suddenly. However, in his last letter to me he enclosed graphs of the output of the various models of alternator, fitted to the Velocette LE, and mine, being ex-police, has a higher output at 6V than the standard alternator and performs very poorly when converted to 12V. I was going to ask him to explain further but that, of course, is no longer possible.
I have had the flywheel magnets remagnetised and this evening started the bike after its rebuild. The voltage from the coils at idle showed around 10.5V. I was not able to measure the output at higher revs due to lack of time, hands and enthusiasm.
I have this evening been told where I can find an off the shelf 6V regulator. I will know for sure tomorrow. In the meantime I thank you all for yoru interest, advice and comments and will keep you all posted (if I haven't already bored you to death).