‘65 was the last 6-volt. My 69 has a 6-V starter, however.
It takes a change of the flywheel gear, and a different bellhousing starter-shaft bushing. No changes to the electric system, but the 12V really whips over that 6V starter motor!
Back in the 60s, I worked summers at my older brother’s battery rebuilding business. For some of the older Detroit tanks that had big engines and a 6V system, we’d cut down a 12V battery to make an 8V, and install that along with a resistor in the rest of the circuits...or not, depending on the owner’s choice. If not, the headlights were amazingly bright, but had to replaced fairly often. At least the engines would start reliably.
From what I can tell, 1966 was the last year of the 6 volts with 12 volt coming in 1967 and the new sealed beam head lamps.
The best part of these things were the suspension. Torsion bars in the back and torsion leaves in the front. Incredibly durable on and off road.
They were great little cars to play around with and sipped gas. I’d like to have one now in a “Baja” kit for running around town.