2004 Cadillac SRX Horn Doesn't Work

There is also a relay in the underhood fuse box, check to see if you feel, or hear that relay click when the horn switch is pushed. That will validate that the control is working, but that don't necessarily mean the relay is good. You can swap it in that fuse box with one that has the same numbers on it, there should be more than one of the same. Next I would go to the horns, the assembly is shown to be under the left headlamp. Raise and remove the front lower air deflector, check for switched power and ground at the horn connector when the switch is pressed, this validates the circuit, and condemns the horn assembly. You can use a test light across the horn connector, if it lights, switched power and ground are present. Often times the horn gets water in it, and eventually fails.