check the battery...or you can goto www.vwvortex.com
If it is completely original it would be 6v, VW changed to 12v in 1967. If you aren't sure if it has been converted look at the battery. Pop off the vent caps, and if there are 3 holes it is a 6v battery, if it has 6 holes it is 12v. If the car is already running you can also just start the engine, and use a multimeter to measure the voltage across the battery. If it reads 12-14v it is a 12v car (the higher reading is the charging system charging the battery). If it read 6-8v it is 6v. If the car doesn't run and the battery is missing, you will have to see if you can find any model numbers printed on the generator or voltage regulator and research them to see if they were used in 6v or 12v cars. http://www.thesamba.com is a good resource & forum ofr air-cooled VWs.
All Harley Davidson motorcycles have used a 12 volt battery since 1965. Prior to 1965 they used a 6 volt battery.
To Tell the Truth - 1956 1965-04-12 was released on: USA: 12 April 1965
To Tell the Truth - 1956 1965-07-12 was released on: USA: 12 July 1965
To Tell the Truth - 1956 1965-12-13 was released on: USA: 13 December 1965
To Tell the Truth - 1956 1965-12-20 was released on: USA: 20 December 1965
To Tell the Truth - 1956 1965-12-27 was released on: USA: 27 December 1965
To Tell the Truth - 1956 1965-12-06 was released on: USA: 6 December 1965
It'll say 6v or 12v written right on the battery.
Gilligan's Island - 1964 Don't Bug the Mosquitoes 2-12 was released on: USA: 9 December 1965
12 volt
you can just check it properly... (on every battery volt is surely given...)
12 volt