Fire wall above starter Most of my trucks have two horns in that location Might be a Canadian thing, Also some Canadian gmc have one on manifold and the second is alone up on the fire wall Likely it was a new requirement at about that time and a late factory addition/modification When the truck has two horns they are hi/low notes just like the modern horns today. There is a special bracket for the dual fire wall horns Also when a truck gets two horns it got a factory horn relay installed next to the tiny fuse box on the fire wall GM did not try grounding out two horns in the steering wheel. -s
