Technical purpose of the diagnostic plug on the code box?

[Prawny12009]

The code box wiring has a green? wire that goes to a 3 pin diagnostic style plug the other wire on it bridges back to earth.

Is this plug used to interrogate or program the code box?

 

[varesecrazy]

Without a photo..

Im guessing that is the OBD1 Generation 3pin diagnostic port

 

[Prawny12009]

Same type of 3 pin plug that is found next to the ecu but this one is down by the code box, only two wires connected one of which is earth.