have a look here,
http://www.powerdynamo.biz/deu/systems/lists/yamaha.phphttp://www.roadandraceignitions.co.uk/http://www.rexcauntracing.com/pages/ig_bsa.htmlI would recommend the Power dynamo/MZB systems as I have fitted them to bikes before and they are very high quality. Although there isn’t one listed for your exact model the later DT kit may fit or if you can have a good read of their site, they say they can make a system for you if you provide them with some information.
How much power do you need?
If you just want a 12 volt light then quite simply stick a 12 volt AC regulator on and that’s usually all you need to do.
If you need 12 volt DC to run a DC ignition, then that’s an entire different kettle of fish. You DT would most likely not have enough power to efficiently run a DC system and a 12 volt regulator/rectifier so you would need coils rewound for more out put, or a different stator or even a better flywheel.
I would highly recommend
www.bettabikes.com they will have answers for you and can even build you a system from scratch or modify your existing one.
having mucked around with suzuki electics for a while, i have found most of the crank tapers are the same, so the yamaha DT crank shaft ends could also be the same for most of the range.