Hi Chris,
the bike was running at 12v as all the bulbs are 12v
That's "12v"
DC (Direct Current). Nothing to do with the alternator, which produces AC (Alternating Current). As you've posted that your bike has a separate rectifier and Zener diode, the rectifier turns (rectifies) the AC into DC and the Zener regulates it, by converting AC more than a little above nominal (~15V on a "12v" system, ~7.5V on a '6V' sysrem) into heat.
Note, just for cheapness, a single Zener must be connected on the DC side of the rectifier but, when two or more are used, they can regulate either the AC or the DC.
Digressing, hopefully for greater clarity:-
. When your bike's existing alternator was connected originally, the original bike's electrics were 6V DC. As Zeners weren't available 'til the mid-1960's, and then only 12V at first, 6V regulation was by the battery and a complex set of connections through either a PRS8 combined ignition and lighting switch, superseded in the early 1960's by separate ignition and lighting switches like 88SA and 41SA. Only the ignition and battery-charging current were rectified, the headlamp and 'emergency' ignition (separate position on the ignition switch) were supplied raw AC direct from the alternator stator.
. One of the reasons British motorcycle makers changed quickly to 12V electrics in the mid-1960's was that availability of 12V Zeners - simple and reliable, they allowed deletion of the complicated AC/DC supply circuitry and substitution of the complex switches by simpler (cheaper) ones.
all 3 wires were being used
The original reason for 3-wire single-phase alternators were the stator coils were divided into 'ignition' - connected by the Green/Black wire to one side of the rectifier, output then rectified to DC to supply the ignition and charge the battery - and 'lighting' - connected by the Green/Yellow wire direct to either the ignition or lighting switches, to supply the headlamp, and the ignition from the 'emergency' position on the ignition switch. Green/White (or White/Green) is common to the other ends of both divisions and is connected to the other rectifier terminal.
When Lucas and the motorcycle makers changed to 12V electrics, they still continued to use the 3-wire single-phase alternator (by then the RM19 and RM20). Different motorcycle makers used slightly different configurations, the simplest of which was to connect the alternator stator Green/Yellow wire to the same rectifier terminal as the Green/Black, thus rectifying the AC output of all six stator coils to DC at all times. The only major reason I know of not to this is if your bike uses a magneto for ignition.
When Lucas superseded the RM19 and RM20 with the RM21, 22 and 23, the latter were still six coils and single-phase but with only two external wires (Green/Yellow and White/Green); what had been separate stator coil connections to be made externally as a motorcycle maker decided were simply internal.
what is the best model for me to get using the rest of the kit already mounted
I'm assuming the existing rectifier has four terminals (if an original with three almost-circular plates mounted on a central stud, the stud itself is the fourth terminal)? If so, as posted already, you're limited to 2-wire stators.
power output will be very low from this type
Not so. As I posted earlier, the RM23 produces 14.5A @ 5,000 rpm (Norton quoted 15A @ 6,000 rpm) and some of these stators might still be available. In any event, Wassel (aka "Genuine Lucas" :rofl) offer alleged '16A' and '20A' pattern versions, though without any rpm qualification and afaik no-one who's tested one has seen these Amps at any rpm a Britbike can manage without converting to a 3D version of the parts book ...
Nevertheless, any will produce considerably more than the existing alternator ...
If a dealer like
Grin can't turn up what's now known as a 'Made In England' RM23 stator (Wassell's licensing agreement with TRW - the owners of the "Lucas" brand - forbids use of the "Lucas" name to advertise components not made by Wassell
), the Wassell "16A" 2-wire stator is as good as it gets ... :bluduh I advise against the "20A" version simply because a Zener's only good for about 12A~12.5A; the ignition coil(s) of a running engine consume(s) about 4A, 16A less 4A equals 12A ... Ish.
if you can't return your new stator to the vendor, can it work with your rotor ?
In this case it's possible to connect 3 wires of your stator in the way it works as 2 wire stator.
Problem with that is, as I posted earlier, given the stator Chris is working with has non-standard wire colours, will be working out which wire is connected to the 'ignition' stator coils, the 'lighting' coils and the 'common' one.
If all the stator coils are all the same resistance, the 'ignition' coils' resistance
should be be half that of the 'lighting' coils'.
I can write up the test sequence but, even then, the stator could well be not particularly powerful.
Hth.
Regards,