LOL i slapped this cheap setup in my old civic. just removed one of the horns to make it fit under the hood.LOL
http://youtu.be/ZDGB-4E9rdY
i just used a 2-3gallon tank what ever it was a fitting to hook up to the shops compressor and a push button switch on my Ebrake handle to activate the solinoid on the horn. worked just fine. just had to refill quite a bit when playing with it! LOL
now my truck i have just normal semi air horn single. i was going to get a second one eventually BUT i think ill just hold out and try to wait to snag a train horn some day! this time ill go real NATHAN because the cheapass train horn just isnt as nice as a real nathan!
i thought i had a video of my semi horn but i cannt find it right now. not sure where that video is anymore! its nice but not enough IMO
if you on the cheap simply buy a air tank and a fill port of some type... you can get tire fill valves so you can air it up at gas station.