A similar discussion popped up in the Fiat500usa forum last year, to no avail.
Here is one person's answer, however:
"There is an interior fuse panel located on the driver's side under the instrument panel that holds 14 fuses. The under hood fuse box we looked at yesterday, has a chart on the fuse box cover. Once you remove the bolt that holds it shut you will be able to see the chart. In your owners manual on pages 58 and 59 are the corresponding charts so you can match the fuse with the issue and simply replace it. I also discovered that with the FIAT 500 app on your iPhone you can go from the Menu to "Vehicle Maintenance" then "Fuses" and it gives a list of possible problems such as: "Horn Is Inoperative" and it will give you fuse location, cavity #, Amp, and color. I thought that was pretty cool! "
Join the conversation at: http://www.fiat500usaforum.com/archive/index.php/t-3270.html?s=4b1cdd37f2de23fe0960205f487c5520