In my younger days I was a VW / porsche guy (a new one was $6000 then)and lots of 6volt cars were converted to 12volts. Some people never changed the starter and only changed the bulbs as they burned out. Very bright while they lasted but we are talking double the volts; way more than 6 to 8. I personally lived in Kansas in the 70's and drove an air cooled car with no choke so I know about hard to start. One winter I was trying to get it running and thought I'd change the spark plugs. No garage so I bundeled myself up like an Astronaut and was fishing around and dropped the wrench. I had to take my glove off to get it and then the dam thing froze to my hand. Great fun. Plus the car wouldn't run at low RPMs, even when warm (which it never got). About 2500RPM it would catch and in the summertime it would burn rubber; not the best on a shiny white road covered with ice. I was thinking about mounting headlights on the doors because it was preminately sideways.
