On the Fiat 850 Facebook page owners regularly ask for a wiring diagram for a Fiat 850. And I have one. Because those posts tend to disappear completely after a week or so (and with that the link to the information) I'll post the wiring diagram here (for a 1967 Berlina).
For other 850 (models the PDF's can be found here:
Fiat 850 Special (in English)