Before carrying out electrical diagnosis, first of all, it is necessary to check the fuses. Remove the wires from the horn connection point; the wires should be connected through an electrical connector. To check the horn, attach battery voltage to the horn terminal with a jumper wire; if the horn does not go off, replace it. If the horn shall sound, then probe for the voltage in the terminal when the horn button is pressed. If there is voltage in the terminal, suspect a poor ground at the horn. If you don't get any voltage at the horn you should look at the 
Relay. If the relay seems to be good, test voltage to the relay power and control circuits: if neither is getting voltage, check the wiring between the relay and the fuse panel. If both relay circuits are getting voltage, silence the horn button and measure the circuit from relay to the horn button for ground. If not, look into the circuit for an open; if there's no open circuit, then change the horn button. If the continuity persist to ground through the horn button, you should look for an open or short in the circuit from relay to horn. There are two horns: on the one hand, it is mounted behind the left 
Headlight assembly and on the other hand it is mounted at central part of vehicle in front of the condenser of most models. To get to the horn located in the center of the base, the bumper cover has to be disconnected. Lift off the nut and bolt and advance the wires to get the left headlight housing out consequently we have access to the left horn. If this bolt is removed, installation is the reversing of the removal process followed by reinsertion of the bracket bolt as a final step.