Where is the horn fuse under hood for 1989 Jeep Cherokee?

There isn't a single, dedicated horn fuse in a 1989 Jeep Cherokee's under-hood fuse box. The horn circuit is usually protected by a fuse that also protects other circuits. You'll need to consult your owner's manual's fuse diagram to identify the correct fuse. The horn is likely protected by a fuse within the main fuse block under the hood, but the exact fuse number and its associated amperage will vary depending on trim level and options.