Sound the horn by pushing the center of the steering wheel. If you have the optional air horn, it is controlled by a cord that you will find up above and to the left of the driver. The harder the cord is pulled, the louder the air horn will sound. The air horn works only after the air brake system pressure gets up to about 115 psi (790 kPa). The air horn will work properly unless the air brake system pressure drops below 60 psi (415 kPa).