D2 5U Battery

I have always been told the starter does not know the difference; majority were set up as positive ground. It would be important if your charging system (if any) was intact and functional. Many of us will just use a 12V battery, as 6V are becoming scarce; just don't crank on it for long periods of time! JM

Yes That’s correct on the starters I do have some old antique farm tractors and converted them to 12 V. All of the wiring for the pony appears to be all original and intact.

Negative Ground system.
Where are you located?

I would take a look at the battery cable ends, the positive terminal is the larger one. Not always 100% correct but you would at worst be connecting it up the way it was used last. Good luck, Mike

In general 6volt systems are positive ground on most other (non Cat) makes and 12 volt are all negative ground. On 6 volt the difference is the charging system regulator if it is positive or negative ground

Cat 6V systems are NEGITIVE GROUND!!!!!!!!!!!!!

Negative Ground system.
Where are you located?