Hi Alfa2001,
This gets very interesting. Assuming they go by ISO 9141 (K line) it should be possible to plug to the K-line pin (23).
Now, as I went through various sources, it seems that a protocol conforming with ISO 9141 could be either one wire (K line) or two wires (K line + L line). Since I do not see any hint of the L line maybe it's one wire type.
Also, your last picture shows that pins 13 and 23 are jumpered and the pin out shows them separate. What do you make of that?
This is what I found in some Barchetta Service Manual, unfortunately they do not give specific location. I will have a look later today if it's there somewhere.
Edit: I missed it the first time I went through it. The L line is supposedly there. Could it be the pin 13?
Edit: Another random find on the internet. Seems to be some FIAT standard 07273 that regards implementation of the ISO 9141 standard. The version referenced below is July 1999.
Not sure if we should interpreted it as all vehicles starting from 1997 have ISO 5: K line + G line (ground?) so all before that used to have ISO 8: K line + L line + G line.
What do you guys think?
EDIT:
Finally, empowered by all the information we've shared here I was able to find this plug! The wires colors are exactly like in JMSG's picture: white with red stripe, black and the remaining pin isn't wired. The connector is the 3 pin type as in other Bs. I haven't tried connecting yet, but I will give it a try on the weekend and then I will let you all know the results.
It was not that easy to find it as the wire harness was pushed underneath of the plastic padding so it was practically invisible. Being patient enough it can be found and pulled out. Just trace the wires as they go out of the ECU. Here's the picture as a proof