Packard Don wrote:
Most of the overdrive electrical components are for 6v so to switch to 12v would require a custom solenoid (if such a thing is even possible) and a full rework of the relay's innards. I governor shouldn't care about the voltage but I'm not sure. You might be able to get by with some kind of voltage step-down device but it seems to me that it would be easier to keep it 6v, then use a step-up for any 12v items you may want to add.

Reproduction wiring harnesses are available and, as 6 requires a larger gauge wire than 12v, you could always do it stock now, then make the switchover later without having to make changes to the harness.