what thick wire are you taking about?
Green only goes one place.......from alternator field (push on flag connector) to the VR. If you have a factory VR the other wire (blue) is switched 12V from the key and is a branch of the same supply going to the ballast resistor. In other words this is "ignition run" voltage coming from the ignition switch, through the bulkhead, and branches off, feeding the ballast and the VR
NOTE!!! THIS VOLTAGE IS NOT PRESENT during "cranking" using the key. There is/ was a second wire (look at your diagram) brown, IGN2, which comes off a separate contact on the ignition switch. THAT powers the coil+ during cranking and bypasses the coil resistor