horn and radio

Check for power at both sides of the switch and then at the accessory. Verify the grounds are good.

Horns go bad all the time, work on that last. Which radio, VHF?
You need to take a look at the back of the radio and find the power and ground wires, probably red and black. There is a chance that the red wire has an inline fuse along the wire run. Where is the radio, under the helm, flush mount at the helm or perhaps up top in a electronic box.. Based on where and how the radio is mounted, the folks on this site can give you more detailed instructions of what to look for.

Fuses should be in the panel under the dash on most. Both are items that tend to need replacement at some point on these boats - especially if at the hem (weather).