Finally found something with Google. From the Monte SS Forum:
Q: There's a green connector in front of my carburetor that is not connected to anything. What is it and what should it be connected to?
The Green wire/connector on the front of the carburetor is a diagnostic connector and is normally not connected to anything. This is where you would connect a Dwell meter to monitor the mixture control solenoid within the carburetor.
sorry for the necro post. I wanted to also add that there was a counterpart Green terminal under the dash. On the passenger side. If you grounded it, it would flash the check engine light and display status information. One of the earliest feedback systems in existence. (at least my 1979 C4 system was.)