There is a pic in Bruce McCalley big book Model T Ford.
The bulb horn was on early '15 model year prior to Jan 1915. The tube ran at the base of the steering column on the right side.
The bulb horn mounted in the same place as the magneto horn, bracket about in center line of the spark and throttle rod springs on the column, on the passenger side of the column.
Photo is the passenger side, the horn would be on the opposite