1991 Honda Civic Si Horn Malfunction

When I push in the horn on the steering wheel, the Door/Seatbelt light comes on and beeps but the horn doesn’t work. Any ideas on how I could fix this?

Start testing components. Test the horn itself; if it works, test the horn relay, and keep going until you get through the entire system.

Did you check the fuse?

There is an electrical short between the two circuits. You need to check each circuit with an electrical multimeter and the wiring diagrams.