I finally took the plunge and purchased a VAPE (formerly Powerdynamo) 12 volt conversion for the old 400. The lights had quit working years ago on this one and after numerous attempts to wind my own lighting coils, I gave in. We had these bikes back in the late 70's and on, I bought this one in October 2000. The kit comes with a new rotor, stator, ignition, regulator, coil and plug wire. Even a new puller for the rotor/mag. The kit is bolt on and fairly simple. The bike fired right up and everything works. I bought an expensive 1157 LED bulb for the tail light/brake light bulb (all the bulbs were changed to 12 volt awhile ago) since the video which has pretty much eliminated the blink when I hit the brake (there is no battery).
The kit was kind of expensive at about $560 but it appears to be a quality item and everything works. It's only money. The old KZ and Spectre getting a little break...
here she is...
(233) 1975DT400B is finally 12 volt! - YouTube