Ditto! There is nothing simple or uncomplicated about a series-parallel switch- - - -I used to service them when I ran a truck shop, plus they're designed for 12/24 volt systems, not 6/12. The 6 volt starter will live a long time on 12 volts, and swapping the rest of the system isn't too difficult. Add a 12 volt coil, and a self-regulating alternator, the above-mentioned resistors for gas gauge and heater blower, and the rest is just bulb changes.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!