Hi,
BJM68,
Every Cub made before serial number 224401, which was in 1964, had a 6 volt, positive ground electrical system, if it had an electrical system. A few Cubs were made without any, just a magneto.
Someone has connected yours with negative ground. They could have just connected it with negative ground, and everything is original, and supposed to have positive ground, or someone might have replaced the generator.
It should have a 4 position light switch, which also controls the charging rate, if it is the original system.
Here is a page from the Cub owner's manual showing how it originally looked under the hood.
The 2nd page shows the 4 position switch, and how to work it.
Below that is the whole 1950 Cub owner's manual, it has lots of info about operation, maintenance, and lubrication. The experts on here recommend that people read it, if you never have. There is a 1949 owner's manual, but the pics in the 1950 are better here on the internet.
http://farmallcub.com/rudi_cub/www.clea ... e%2033.jpg
http://farmallcub.com/rudi_cub/www.clea ... e%2034.jpg
http://farmallcub.com/rudi_cub/www.clea ... index.html