My horn doesn't work?

1040 is the wiring from there back to the fuse. You need to check fuse #3 (15amp) in the engine compartment fuse box. If the fuse is blown, then you could have a short somewhere but try replacing the fuse first to see if the short was temporary. The wiring diagram for the horn circuit is attached below. I would swap out the relay as well.

There is a junction block under the right rear part of the seat. It could also be the module that is under the rear shelf in the trunk. That connects the remote and the steering wheel. However if you are getting power to the fuse then there is a wire that leads to the relay and they or it could possibly be disconnected. Or not make good contact. Unfortunately it's under the fuse block so the bestthing would be to test where #87 is on teh relay with a testlight as that should activate the relay. The relay will be marked on the bottom, it might take a magnifying glass to see it.

Test your horn relay, located in the underhood bussed electrical center (on right front of engine compartment, forward of the strut tower)

Did you check horn relay? If relay and fuse is good then test the horn by supplying 12v direct power to it. If it sounds then either wiring issue or horn pad/switch is bad. If doesn't sound then horn needs replaced. For the belt. Shouldn't have to, that is only required on the malibu and cutlass models. The park avenue should just have to loosen tension and remove belt.