Hi, Gus,
I don't think the green wire is original to the car.
If you follow the wire to its other end, you may find a condenser there.
If you do, it belongs to the later aluminum bodied distributor.
I can see the old type cast iron distributor '051' in your picture but no condenser. Is there one on the distributor? If not, PO may have substituted the later condenser, in which case the wire would have been on the distributor terminal.
Are you still using contact points?
Naj