Yesterday, while driving the Power Wagon, some lovely human being decided to try and run me into oncoming traffic at a merge. Naturally, I laid on the horn, and remembered how dinky the Dakota horns I installed in the truck to pass state inspection were. I mean, the horn on my Kia is much more intimidating. Even my wife started laughing, stating that I wasn't going to get anyone's attention with those weenie horns. And you know what? She's right. These things are lame-o.
So, that leads me to the question: what's your favorite horn? Let's break this into two categories: aftermarket replacements and stuff I can snag at the junkyard.
I remember people in my Subaru Fanboi days fawning over the Hella Supertones. In a car like that they are great, but I'm not sure the tone matches the big, old truck. I'm looking for a basic, two-tone high/low setup that doesn't require much to swap in, so no train horns. 
Used Cadillac 4 note for the big win!
Used out of a domistic pick up truck will probably give you the sound you expect.
LH horns (Intrepid, concorde, 300m) are decent at getting attention, possibly still pick them up from a wrecking yard.
I like the Fiamm air horns.
I had a set of Hella Supertones, and I hated the way they sound.
I like to put a horn from a little car like an Echo in a full size car just for effect.
My preference would be train horns in everything I own
Old American cars had the best horns. The Cadillac one is perfect. So was the horn from my 66 Pontiac. A very meaty attention grabbing sound.
caddy horn:
https://youtube.com/watch?v=sdKJ3ZRKNJg
60s Bonneville horn:
https://youtube.com/watch?v=BITlVcY6FFc
Caddy horns would be awesome, if I can find some. Not sure if I can just hook them up to my current wiring or if I have to add an additional relay; Mopar truck horn wiring from back then is a bit strange, as nothing works unless the ignition is on. We do have a junkyard here in town with some older stuff; sounds like I'll have to take a stroll through there.
In reply to Woody (Forum Supportum) :
That's the point.
Hella, universal, dual note trumpets on Amazon and RockAuto. Play the video, the last picture and see the video in the reviews.
Mr. Peabody said:
I like to put a horn from a little car like an Echo in a full size car just for effect.
My preference would be train horns in everything I own
My Dodge Motorhome has twin Hella horns from a Porsche 911. Don't ask why.
Shadeux said:
In reply to Woody (Forum Supportum) :
That's the point.
Not if I hate them from inside the same car they're installed in.
Twin horns from Chrysler minivans have a pretty assertive honk. Readily junkyardeable, too.
In reply to Woody (Forum Supportum) :
Fair enough, but I want a horn to get someone's attention, not to listen to.
John Welsh said:
Hella, universal, dual note trumpets on Amazon and RockAuto. Play the video, the last picture and see the video in the reviews.
Also look at the Piaa horns. That's what I settled on
Note that some aftermarket air horns are tuned to a pleasing major third, others are tuned to a dissonant semitone. These will leave a different impression on the hornee.
I went to the junkyard once and harvested as many horns as I could off old american iron. I've got three sets of the Caddy quad-tones, they are 100% appropriate for the vehicle.
Woody (Forum Supportum) said:
I like the Fiamm air horns.
Totally agree with this statement.
Semi-related:
I found this 60s-era display model at a non car flea market a few years ago. It sounds great and it's seriously loud.
The B-body Caprice / Roadmaster dual horns. Sadly on my last set currently, need to harvest some more.
02Pilot
UberDork
12/13/21 8:08 p.m.
I put a set of PIAAs on my ND Miata to replace the awful OE horns. Nice and loud, good, vaguely Italian tone. I think I used the 400/500Hz versions.
I'm sure Nick D could hook you up with a locomotive horn. Nobody's ignoring that.
All of my vehicles (even the new ones, except my GTI), have the OEM FIAMM horns that came on most German cars in the 80s and 90s. Because they sound good, and can be found at any junkyard.
Re: the Cadillac horns. I think only one of the four tones is unique to Cadillac, and even then it may not be. I know I was able to mix and match at the junkyard a few years back and get all four of them from separate cars. The note is stamped on the horn. They are probably going in my S10, but there are times I think they need to be in the Miata.
I've got the Wolo Bad Boy horn on my project car:
https://wolo-mfg.com/horns/motorcycle-horns/air-horn/model-419-bad-boy.html
They sell them at Harbor Freight and on Amazon.
