The stock horn is activated when the horn button goes to ground, not by turning power on. The bottom circuit diagram show how to wire it. 30 & 86 should be from the battery. (Fused at 20 amps or so) 87 is power to the horn. 85 goes to the horn button, when the button is pushed it grounds out the circuit closing the relay and powering the horn. 87a (If your relay has it) is not used.
