Workstar Air Horn switch/valve location

This is probly one of the simpler questions asked on the board. Got called in this morning driver runs a 2010 workstar plow truck and the air horn button got pressed getting in the truck and air horns locked on. I looked for a fuse or relay to temporarily disconnect horns but nothing is labelled "horn" would it be powered by the relay labelled "cab aux" ? Also since the air horn is electric over air where would the electric controlled air valve be located? I need to figure out if the electric side is locked on eg switch, stuck relay or if the air valve has stuck on. Considering the weather I had to get it going quickly so I was able to find the 3/8 air line feed above head liner cut and fold line over until the weather clears and I can properly repair. Any advice is appreciated.

 

thanks very much. I did some online research and found that ih is now running the same type of aux manifold as the volvos. If I am correct it will be a rectangle manifold with a air feed and multiple supplies that are controlled by individual electric solinoids all solinoids fed by one wiring plug that plugs in to manifold from body controller am I correct? I will look in frame for the valve this week thanks again.