I got a 8" PA horn from Radio Shack on clearance for $8. It's loud as hell.
Before that I used a 4" or 6" horn from there also. That one was pretty loud. Make sure you mount it as far away from the mic as possible (e.g. front of the passenger side fender under the hood).
82 Wagoneer Brougham 3126.96.36.199x2<br />63 Honda CB77 Superhawk 305 for sale!