I'll give this a shot, although I explain things terribly sometimes. You should have a small tab on the base of the shaft tube. It would look like a tab for an electrical connector to slide onto.
The follow the negative (-)current path......
It starts at the grounded steering box itself. Then uses the small wire to jump the rubber donut, where it (the neg charge) is taken up the center of the shaft to the horn button via a wire. The wire is attached to the horn button. The horn button is two pieces that are insulated fom each other until they are pressed together. So when the neg charge travels to the horn it sits in the center section until such time as the horn is pressed. When that happens the inner section of the button contacts the outter section which transmits the neg charge into the steering column tube. It travels all the way down the outter tube to the little connector I mentioned in the beginning. Then, via a wire, it travels to the horn (which has constant 12V +) and provides the neg to complete the circuit.
You can also use it to provide the neg to activate a horn relay if you choose. Same principle but you would ground the horn. Run a wire from the pos supply tab on the horn to the relay. Bring pos + to the relay, and use the neg - from the steering tube to complete the relay circuit.
You need to be sure your steering tube is insulated from any ground. On my Speedster I placed a section of rubber stair tread between the mount and the frame, used nylon bushings around the bolts, and nylon washers under the nuts. Use either a contuinity meter or test light to ensure the tube is not grounded.
