Done some searching.....and it looks like it's an Alfa/Fiat special. My 145qv had the same plug fitted....and the previous owner had to cut it off to fit another stereo. It came from the factory with this type plug to Sony harness. I've got a Cinquecento in Spain, and just got a mate to check it, and it's exactly the same plugs, just with 2 speaker pins less (as mentioned above).....the rear speakers are run in series from one cable. The Cinq has an adaptor cable to ISO....with a Fiat label on it....looks like a typical Fiat/Alfa use whatever they had in the parts bin job....probably didn't have any ISO plugs so bunged these in....doesn't surprise me....the original 1.1 engine in my Cinq had an 866 cam fitted from factory.....whatever they had in stock at the time.