Horn wont work...1999 cutlass

easiest is chevy pumps hum and relays click so turn key on and listen should hear click and then a slight hum when pressuring up --no click can mean relay bad or over heated but tech way is remove relay and test with a meter or use another [same number relay]matching relay and turn key and if starts relay bad no start check the pump for power possible bad harness wire or connection or pump bad

You could pull the horn fuse, that should kill it. The horn fuse is hot all the time. Two possibilities, one is security system, the other is problem with horn switch or wiring in the steering column.
The horn switch is ground for the control side of horn relay. Part of key fob security horn beep, is also a ground wire. In the diagram, you can see the two wires, The one for fob, take it loose, see if that stops the horn sounding by accident. Don't leave any live wires hanging loose, use electrical tape or something to insulate. I don't know if taking that one wire loose will cause any problems or not, I guess you can try it and see?
Of course, you still want the horn switch to work normally.

push on the horn button you should hear a click noise. is so then the circuit to the relay and the relay is good. then you find the horn and check for power to the horn with the horn button pushed. if you do then the horn is bad.

Maybe the horn relay is stuck or the horn switch is bad.

Did you check the horn relay! it is in fuse box under hood. God-Bless! if the relay is bad horn will not work. It should be be behind or near the passenger side head light.

take a multimeter and check if your getting power to the relay and from it (when its supposed to be on). if no power to relay its the switch that activates relay or the wiring, if no power from relay when its supposed to be working, bad relay.

Relays fail quite often and are easy to replace, while the button seldom fails and is much harder to repair. Start with fuses and relay.

Many of the relays in a car are exactly the same. Look for a similar one and swap the two, that will tell you if its good or bad.

as with all elect. fails check all fuses
in this case the 15 amp fuse marked, HORN
can i presume all else works good> car drives.?
all answers, USA spec car. nobody ever tells location, so..... if not USA< all answers wrong. the usa car has just 1 horn.....
got voltage to horn? 12v
Yes or no.?
if yes horn bad.
got voltage from horn relay
yes, bad wires.from, relay to horn
no, got voltage 12v to horn relay coil,
yes, good, no bad fuse.
got 0v to other relay coil (all tests honking)
yes, bad relay.
no, bad horns switch.

if you want me to guess. sure.
1: bad wires ../connections, end to end.
2 bad horn
3: bad relay
4: bad horn switch.

new horn or relay gone most likely but make sure it is grounded good or wont work either hook battery booster cable from negative battery terminal to horn bracket if it works then clean mounting area under horn ground is bad