I could be any number of things. With a METER, check for 12V at the horn when the horn button/bar is pushed. If you have 12V, try running a ground wire to the horn from the battery, (clean up a spot on the mount to touch it to). If that works take the horn off and clean up the ground connection. If no 12V and you have cruise control, you have a horn relay. Also if you have cruise control, the horn relay is grounded through a brush in the steering column, if that one is bad, your cruise control should also be failing.
Good luck,
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