6 volt alternator

[larry/Texas]

I have purchased a 6 volt single wire alternator to install on my '33 with a '38 engine. I do not know if it is negative or positive ground. How do I verify so that I do not have a problem when I try to start the engine. Battery is currently six volt positive ground. I have been told that not changing a 12 volt system battery to negative ground will fry the wiring so as you can see I want to be careful and do it right the first time.

Thanks for your help.

larry/Texas