The NSU electrics are finally fixed (hopefully) stopped trying to sort the wiring (all the same colour and nothing marked). Threw it all away and started again without the “chocolate-block” connectors, sticky tape etc. Sorting the dynamo proved to be somewhat more of a problem, the regulator/cut-out didn’t work and finding another for a 70 year dynamo was not going to be easy. Spent along time “chasing rainbows” diodes, relays and a cheap German regulator that was said to be just the thing, only it wasn’t. Bosch dynamos are wired differently from say a Lucas as they have earth side regulation as opposed to live side regulation which makes regulator you buy here unsuitable. However I discovered that it was possible to rearrange the dynamo’s internal wiring to the Lucas style. Thus ordered a unit from a well known British supplier of M/C parts
No names, no pack drill, but I’m sure some of you will recognise it, I won’t be buying another one. It turned out to be just as useless. In the end did what I should have done in the first place and bought a DVR2. They are not designed and will not work with Bosch dynamos, but once the internal wiring was swapped round it work just fine.