For the 1994 Chevy S10 Pickup horn circuit we have a "HOT AT ALL TIMES" 20A HORN/DM fuse supplying the horn relay coil and contacts located in the convenience center behind left side of I/P with an orange wire. The black wire runs from the relay coil to the horn switch. The dark green wire runs from the relay contact to any number of horns.

Measure DC voltage from the relay black to ground. 12v=horn switch (button) is not stuck. 0V=horn switch is stuck. Verify that pressing on the horn switch always shows 0V.

Measure DC voltage across the relay from orange to dark green. 12v=impossible for you since horns are blowing. 0v=relay or horn switch is stuck. Tap the relay to see if the contacts break free.

Verify the horns stop when the relay is removed.

To keep from waking the neighbors you should clip the test leads in place and insert the fuse briefly to test.

You need to obtain a wiring diagram for your vehicle.