From memory, it is a Fiat multiplug which is an oblong shape with space for 3 terminals but only 2 are used. It should have a hold-on tab on one of the flat sides.
The plug is located in the engine bay at the scuttle. It has a protective cap on it which must be removed before the diagnostic harness is plugged in. I think it is located near the brake master cylinder. The harness for the diagnostic tool should also have an earth wire to connect to chassis earth. The plug is about an inch wide.