Green wires under the hood are usually associated with the AC system.
The Bentley diagrams show an AC "Solenoid" connected to a green and a black wire in dotted lines.
The dotted lines indicate a circuit that may not be present in all markets, world-wide, and not in the U.S.

I don't know what this solenoid (item #106 in the diagrams) does, but it probably is not even installed on your car. So I wouldn't worry about those wires and plug.

EDIT: I now think that (missing) solenoid was a KJet item mounted under the throttle body. When energized, it would increase the idle speed when the AC is activated. Much of the 240 wiring is often "one size fits all", which explains the (unused) mystery wire on your U.S. market, non-KJet 240.

Another typical market-related item is Fuse #6, which (on '86-'90 U.S. 240's) is labeled on the fuse cover as "Main Fuel Pump".

But that is true only in foreign markets where KJet FI is still used in post-'85 240's. There IS power to it (as with all fuses 6 thru 10), but it has no outbound wiring. Consider it a spare on U.S. market cars.

In 1991 however, Fuse #6 does become the Main FI fuse, replacing the 25A blade fuse under the hood.


--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.