You can trace the wire all the way back until it leads you to the relay, or look in the fuse panel... most likely in the one under the hood (as apposed to the one in the dash). Fuse panel is labeled under the cover, and if it's not named, and just numbered, refer to owners manual as to which relay # it is.
If the horn is working, you can touch the top of the relay(s) and feel/listen for the click. (unplug the actual horn if it gets too noisy).
Good luck!
