Done this on my daughter's 1998 1.2 Punto and it is easy. Firstly, go and buy one so you know what it looks like. It clips in to a 'plug' on top of the cam belt cover, and sits lower down looking at the crankshaft pulley - I think one bolt holds it in.
Mr Fiat runs the cable partly inside the cam belt cover, don't bother with this and run your new one externally. Simples.
Vince, October 2010
