I would suspect you have a loose or bad ground connection.
You probably have a short in your electrical system. Also the fuse may be burnt out on the horn.
Electrical problem, Bad button/horn.
This problem may be a bad fuse, or a bad control module. It could also be the result of an electrical short or worn wiring insulation in the circuit.
If you are repairing the horn, you will find the horn housing under the front left fender on the "Driver" side of the car near the blinker. You have to get on the ground to see it.
Horn is located on passenger side front of the tire and just behind blinker light. It is attached to the frame work and if you look up under, you will see the square of the horn pointed down.
I hope you checked the fuses first.
Up underneath the dash on the driver's side are the relays for the door lock, wipers, headlamp, horn and flashers. They are together in a single cluster.
An electrical problem.
i had the same problem with my truck, electrical problems are the usual thing you should expect, you may want to check the battery first then the rest of the wiring, usually there is a wire on the passenger's side of the radio that comes out a little causing a short, that maybe the problem with your electrical components, if your truck doesn't start, try getting some electrical wiring via a cable and touch the wire to the + side of your battery and to your starter, be careful, there will be a big spark, but if it sparks so much that it burns you, try another spot.
a dead battery
You might need to refill your blinker fluid. If that does not work, check above the passengers visor..
The horn on a 2000 Ford Explorer could go off due to several reasons, such as a stuck horn relay, a malfunctioning steering wheel switch, or a short circuit in the wiring. Additionally, moisture or corrosion in the electrical connections can cause the horn to activate unexpectedly. If the horn sounds continuously, it may indicate a problem with the vehicle's alarm system or an issue with the vehicle's electrical system. It's advisable to have the vehicle inspected by a qualified mechanic to diagnose and resolve the issue.