You didn"t mention it but your horn should work through a relay so when the button is pushed the ground in the cloumn is applied to the relay and the horn works. Your horn is actualy two circuits one for the horn and one for the relay. They may both be on the same fuse. If you ran the horn directly off the column you'd need a #14 or #12 wire and the horn button switch wouldn't last long. Anyway there shouldn't be any + volts in the column for the horn.