I finally got around to making a proper schematic of my air horn wiring, including the Highway / City toggle switch that determines whether the steering wheel horn button blows the stock electric horns or the air horns. My diagram includes 4 selector toggles, but this is because I'm putting together a setup to demonstrate multiple horn and siren devices. Normally, you would have only one air horn solenoid connected to the 30A relay.

The schematic:


Below is what the panel on the dash really looks like. I cut a piece of aluminum flat stock (what auto customizers mistakenly refer to as "billet") and polished it to make a simple panel to cover the useless slot in my aftermarket stereo adapter bracket:


Compressor and horn in the bed. Compressor is oversized (30 gal) because I test some large horns. For regular truck air horns you only need about 5 gallons:

 

Wow, that is some set of horns. Looks like you did a great job on the wiring and panel. Nice one.

 

What are those 3 note horns from and the compressor you use?
I have a airraid siren sitting in my driveway, fire it off on New Years.

Ever have the urge to fire off the horn at some offending boom box car beside you at the stoplights?

 

Here's a follow up, the horn is now operational and I made a test video. Because my camera has automatic gain control you can't tell the relative loudness of the stock horns vs air horns, but the length of the echos is a clue. I have to wear the earmuffs in order to honk the horns while I'm standing next to the truck :-)

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