The dynamo will come off the housing, if that's the part you really need.
That three wire dynamo was only ever used on the Very early B7100, and maybe the early B7001's.
I don't have a wiring diagram for the very early B7100's that took that 3 wire dynamo.
I don't think a WSM (aka service manual ) exists that shows the three wire set up.
But it memory serves me correctly one of the leads feeds the lighting circuit directly.
You could easily trace the wires back to the regulator and figure out witch 2 go there and hook those up then find the other end of wire 3 and tie it back to a switched hot for the lights.
EDIT: Little search and found it, yes it does feed the lighting circuit so my fix to turn it into a 2 wire unit will work.
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