Neutral:
- If a two-conductor cable was laid in advance, you have to somehow lead mass to the other contact. Either, they laid a two-wire cable to the Dynamo (rather expensive) or you put a short piece of cable from the ground contact on the mudguard (rather amateurish and fragile) or screwing the housing and connects the fixing screw with the earth contact, eg with a paper clip. The latter I have done and works great.
