Just removed the airbox to change the plugs and leads and found this connector attached to the fuel rail with nothing plugged into it. I am going to take a guess and say maybe the connector for cruise control?
Purely a guess as I really have no clue.
1984 5sp

 

That's the crank sensor lead. For factory and dealer use only.

 

Thankyou, at least I haven't lost anything ;-)

 

Sorry, none of us will agree to such a wide open statement