I had one similar to that on a Model A Ford at one time. Given it was over 40 years ago, my faint recollection it was installed between the exhaust manifold and the exhaust pipe connection. The brass pipes were pretty fragile so it was removed. You may be missing a 'T'
fitting for installation. Aeromore was a mfr.of horns like this.

Pictures attached. Can someone tell me a bit about this item. It has three different tones, I held it on the exhaust on my 1929, it works. But, I have no idea what or where it would hook up to,  anybody seen these things before? The item says "Autohorn" on the plate.
Thanks,
SD Glenn