The horn on our 90 Vette stopped working.I cleaned the steering wheel contacts& checked the horn/theft fuse---it's good.If I replace the horn relay & still no horns ,what else can cause this problem? Thanks for any help.

Besides the horn/theft fuse which you've checked--there is also a 5 amp fuse labeled LCD in the main fuse block on the passenger side end of the dash--check that and be sure it's good. It supplies power for the "pull in coil" of the horn relay. If that fuse is good, have someone push the horn button on/off/on/off while you touch the horn relay to see if you can feel it clicking. Post back with what you find.

i would also check the grounds on the front frames of the car. vettes are notorious for bad grounds.