I don't know your car, but I do have a 1971 Volvo with what should be a similar setup. The green wire you have from the coil - to the distributor has been added to replace the wire that goes from coil - through the tach and then to the distributor.

Try to find the wire that comes out of the tach and to the dizzy. You can then disconnect your green wire and use the circuit through the tach.

Rolfe
'71 volvo 1800
'98 sl500