Most boats don't have fuse boxes. While it would be a great idea, it does create more wiring to route it all to the box. So anything requiring a fuse will have it in line. Typically you can find a main fuse or breaker somewhere near the battery but obviously that's not the issue for individual items not working.
For pumps. It's likely that the pumps have clogged, failed, or the switch for them is bad. If there are multiple pumps and they all quit at the same time, I'd look at a switch issue.
Same with the horn. Most horns are simply run straight to the main power block so if it's not working it's the switch/button or the horn or a connection.
I am speaking in general boat jargon. I don't know specifics on this boat.