I believe the wiring on my bike was totally standard, except a 6v regulator was fitted to the back of the headlamp. This was just for the AC 'headlamp' circuit.
Now, I've fitted a Rex SpeedShop complete electronic ignition / 12V system - and obviously removed the 6v regulator. The conversion kit was plug and play. It came with a new rectifier/regulator to replace the old rectifier.
Is the new rectifier/regulator just for the DC circuit? ie, Is the AC 'headlamp' circuit still not included in the new rectifier/regulator circuit? Should I buy a new 12v regulator for the AC 'headlamp' circuit (to replace the old 6v regulator).
I've attached a diagram to show the AC 'headlamp' circuit and the DC circuit.
Many thanks................ 

Hi Jammyyammy, I bought the 12v lighting/charging coil conversion from Rex's for my bike, although mines a 75 DT 250B.  You only need the ONE 12 voltage regulator/rectifier supplied by them.  The VR controls the AC lighting circuits you identified in your drawing by simply 'T'eeing into the headlight circuit which is typically a Yellow wire.  The rectifier converts the AC charging supplies (Green/white for daytime running - key position 1 or Green/Red for nightime running - key position 2) to DC at approx 14.2Volts which then charges the battery.  The standard DC system on your bike is not hugely load sensitive and a good battery can easily accomodate the small load changes involved and hence does not require regulating.

Hope this helps. Andy. 

Many thanks Andy for responding. So the new 'combined' regulator/rectifier is housing two independent items on different circuits?

Yep, that's exactly right. It regulates your AC lighting supply as one task and it takes the AC charging supplies, converts to DC and this supplies your battery as a second task. Best regards Andy.

Thanks Andy - I fully understand now...

Curious if you had to replace the headlight for a 12V unit as well?  It doesn't look like Rex's includes a headlight in their kit

Hi 'Rotten Eggs'.  O.K. before I go any further I'm sure everyone wants to know how you came by a name like that...?  

I'm assuming you were maybe after a 5 3/4" replacement headlight for your resto ?  If so the link below may be helpful.

www.rexs-speedshop.com/product/xt-dt-h4-headlamp-conversion/

Hope this helps.  Andy.

Hi - I bought a Lucas LUB223 off eBay for £24. It takes the H4 bulbs. The bike isn't quite on the road yet, but my plan is to take it for an MOT and ask the tester to check / align the headlight. I just noticed that the Rex's speedshop one has a 'sidelight'. The Lucas one doesn't have that...

The side/park light was not fitted to North American models.

If you have the US ignition switch, it won't be fitted with the blue/red wire that operates the park light.

got my Rex 12V kit and am super excited to fire it up however, after digging into things, now I also need a new LH switch as it looks like the previous owner of my DT 250B did some home wiring to install what looks to be the wrong LH switch thus has the head light running on DC feed off the brown wire .  Anyway while I wait for the proper LH switch to show up. I have a question.  the Rex 12V stator has the Green wire off the lighting coil connecting to the Green/White (day mode - no tail light) , do I need to tie it parralel to the Green/Red (night)  to the Rex stator Green wire as well??, so that the rectifier will be supplied AC to convert regarless of LH lighting switch position?