Hy svwilbur, the "green" wire was used to provide a full twelve volts to the coil during starting, either through the "ign 1, ign 2" type switch, or through the second small terminal on the starter solenoid. The "green" wire bypassed the ignition resistor, by either hooking up to the resistor output terminal, or hooking directly to the coil input terminal. If you leave this wire out of the starting circuit you may experience hard starting problems. A GM engineer once said "parts left out cost nothing, and cause no service problems, so if we put the part in the vehicle, you can be sure we think it is required". Hope that helps.
