Can someone tell me how to wire a Model A horn (6V) to a 12V system. I have built a 31 Street Rod and want the original horn sound. Roger
You need to somehow supply it 6 volts. You could get another identical 6v horn and wire it in series with the current horn, or you could use one of those 6V voltage drop boxes.
Try a voltage reducer. Speedway has several to choose from. Some just run them on 12 volt but they sound weird and I don't know how long they will last.