I am looking for a three hole Klaxton mechanical horn mount that would work on my 1915 Model T Roadster. If you have one I would be interested in purchasing it.
Steve Jelf made this handy mount that requires no drilling.
He might be referring to a Stewart three hole bracket.
The bracket has a 90 degree twist in it so it is parallel with the dummy door. You screw it into the wood behind the leatherette panel. Does not require drilling the sheet metal.
My dad has one on his '17 touring. Unfortunately, I don't have a photo of the interior side in my computer but, you should be able to get the idea how it works:
Ed and Erick do you have one for sell? Please let me know.
Sorry, don't have one for sale.
The bracket that Ed posted has been recently modified - it shouldn't include that large piece of sheet metal that straddles the door.
This is what is should look like. It screws directly into the top of the door. For theft prevention, when you park the car you can remove the horn and take it with you by unscrewing the bolt.