Several people have posted information that they have found dual horns (seashell style) mounted on the inner fender (not the location shown in the factory installation manual).
Can you post a link-to a photo of your mounting bracket(s)? Presumably, it is not like the bracket that attaches to the mounting-boss on the intake manifold (shown by DADS50), nor is it like the one shown in the installation manual?
It should also be noted that 6v seashell-style horns were used on cars - those horns had slightly different mounting brackets and the brackets attached to different bolt-locations on the car horn housings. It is quite possible that someone added car horns at sometime in your truck's life (and might have fabricated a mounting bracket). If you can post a link-to a photo of the mounting bolts on your seashell horns, I can check to see if they match a truck or a car horn. (or, you could compare the orientation of your seashell horns to the brackets in comparison the photo in the installation manual)
