As I said on FB it wont work with the Fiat 500 key.
On the later models the alarm key switch was removed. Not sure how it works but if the alarm key switch is set to on why mess with it? Also wouldn't it be very easy for car criminals to turn the alarm off if all they had to do was join two wires? Maybe??? Hence why it was removed. But I aint got a clue.
To get your alarm rcl working, you need to make sure that your ceiling light receiver is in working order and not knackered. Do the lights flash when you press the small button in?
You need a 4 digit code to a working key to open the alarm system. If not try datarecall (
http://myweb.tiscali.co.uk/datarecall/) he might be able to help at a small price. Or send a private message to reddy4bed on this forum.