I purchased a 1948 chevy 1/2 ton pickup truck to restore. I have been researching the horn and I've seen that the horn is mounted on the manifold. But my truck has a dual horn mounted on the firewall.

Pic: http://www.flickr.com/photos/chucklaw65/7224617886/in/photostream

Is this a dealer installed item? Or did the PO install it later on?

Thanks!
Chuck Law