At first, I was told the unique sound of the horn was caused by pumping 12 volts through the truck’s original 6 volt horn and that the excess voltage burnt the horn out over time.  Since the factory horn was still in place (but not working) when I purchased the truck, I assumed this to be true.

Attempting to recreate the original sound, the previous owner tried several horns.  First an air horn, then an old fashioned “oo-gah” horn with foam in the trumpet to deaden the tinny tail-off sound.  This sounded very close to the original Creeper's Truck sound, but not closes enough for me.  I added an “ocean Liner” horn from J.C. Whitney.  The combination of the two horns produced the closest sound yet to the original Creeper's Truck horn.

To my surprise, I recently learned that the truck’s horn was not used at all during filming and its deep raspy voice was digitally created in the studio.  If you listen closely, you can hear the "Godzilla Roar" sound effect added by the director, as his homage to another great movie beast.