6volt / 12 volt
The WWII MB/GPW models were 6 volt. The Miltiary models after that, from the 50's and newer, including the M38, M38A1, were 24 volt. The civilian models were 6 volt (CJ2A, CJ3A, CJ3b, early CJ5) and Jeep stopped using 6 volt in 1956 and switched to 12volt with the CJ5.
You will find many pre-56 models which have been changed to 12 volt which were originally 6 volt. The quality of the change-over varied. Sometimes thing that should be changed did not get changed, I.E. Spark coil, starter, instruments which might have step-down reisisters, or might not.