Unfortunately, based on what you have told me, I'll have to delete my wiring diagram for the OBD2 port. I don't know what is hooked up to what.
Sorry to hear that. But I took the picture I posted earlier with the 2 ISO connectors by the Motronic. You can see yourself. Can't say if the wiring of M5.2 F355 is the same as 355 F1? You also can open up the cover behind your driver seat (RH of the car) and see which wires you got?
I only have one 3-pin plug. i.e. the one I attach a Fiat 3 pin/OBD2 adaptor & scanner to. Non-N. American cars don't have OBD2 ports under the dash. There is no 2 wire inline plug and, of course, no CAN line plug (for F1 TCU comms) because I have a gated ('98) car. It matches the '97 paper diagrams and my colour diagram.
