To wrap up this thread for anyone reading in the future... I got my horns working very well on 6V (negative ground), so the Autolite HAB60 and HAB61 are definitely 6V horns. Removed the bypass wire from the low note horn, hooked each directly to a 6V battery, and the more I honked them the better they started to sound. Tuned them with the armature screw and then cleaned all electrical connections and grounds in the system. My wife was pretty annoyed that 15 minutes of honking destroyed her nap, but the two-tone symphony my truck now produces was well worth it.
