2007 dodge ram 2500 6.7 horn

ok im trying to install air horns in truck, horn switch located. seems like its a negative triger ???  customer would like a toggle switch to be either air horn or factory. selinoids for air switch need to be positive trigger. how can i do this ?? thanks for all help in advance ??? also do i need a diode to eliminate chirp when toggeling back and forth ?

more info: the horn switch under dash seems to be constant 12 v + (drk grn / purple) until horn button is pressed . it then becomes (- ) and the horn sounds. at the stock horns on the truck, yes there are 2 , one is on with neg trigger the other positive. we would like both oem horns to not sound when the toggle switch is in air horn mode however when toggle is in oem mode we want the horns (oem) to honk as normal. the only switch we want is the oem (steering wheel) to use either horns and the toggle switch to choose either air horn or oem horns. sorry if this sounds confusing.