[bergie]

Just my two cents worth, but my impression is that you have two horns since your post stated "horns". Aren't these normally wired in parallel? In other words six volts is applied to each horn when the horn button is pushed and the return path(ground) is supplied by the mounting bolts to complete the circuit. When converting to 12 volts, all that needs to be done is the 12 volts from the horn button is applied to one horn terminal only and then that horn has to be insulated from ground(no metal contact) and the body of the insulated horn is wired to the terminal lug of the second horn. The second horn is mounted as normal, thus being grounded(current return path) by the metal of the horn body and the frame of the vehicle. You now would have the horns wired in series and each horn is dropping six volts so should sound just as they did before converting to 12 volts. Hope this helps. Some people say water faucet rubber washers work good to isolate the first horn.