Hey Mark,
welcome to fto-ireland!
You can find a description of the fuses in the FTO in the owners manual, which you can download from the downloads page
http://www.fto-ireland.com/downloads.html. Its on page 107 of the pdf file.
According to the manual, the radio fuse is in the engine fuse box, number 5, a 15A fuse. Its kinda hard to tell which fuse is #5 in it though. Maybe if someone has an original FTO manual they'll see it clearer. If its any help, there supposed to be just 3 15A fuses, the radio, the stop lamp and the fog lamp. You might be able to work out which is #5 by following the list of fuses and matching the Amps with whats in the box already?
Kev.