OK, it works!. Recently converted my 53 HH sedan to 12V, but did not like the sounds of the horns on 12v- not just loud, but also pitchy. On another site I got the idea to arrange the horns in series, thus delivering 6V to each. I had to isolate the driver-side horn from ground by wrapping a square of clear plastic packaging (you know, the stuff that cuts your hands as you use scissors to remove a tool or a toy from it) around the horn mount portion of the firewall-to-frame strut, and attaching the horn with nylon bolts. I then ran a wire from the horn body at one of the mounting holes (which made contact with bare metal on the horn) to the terminal on the passenger side horn, which remained mounted as usual. Now I get a nice original volume and tone from my horns.