[puddleglum]

Welcome to the forum and congrats on the new ride. They are cool little cars.
You probably want to be careful with adding a kill switch. If you it you want to make sure that you do it in a way you don't have a warranty fight down the road.
I don't know if anyone's done one on a Fiat yet, maybe, but the plan is generic. Finding a wiring diagram or the right wire might be tricky. Here is the basic idea. You need to identify the common wire that powers the injectors, install a normally closed relay into that wire. You can also feed the relay's coil from the injector power wire. Use some sort of microswitch to open the relay in the relay coil ground wire and your done. I love mine. It is by far the best return of any mod I've ever done IMO.