Hi malcolm,
There should be a 10amp fuse in the interior right-side fuse box under the dash which controls "Audio", fuse No.6 at the bottom of the longest row.
Additionally there are two 30amp fuses in the engine bay fuse box just in front of the battery which are listed as Audio (Radio No.1 and Radio No.2)
I would try the interior fuse as a starting point.
Best of luck.
Dec.