212 Grader: 6 volt positive or negative ground?

I have a 212 1U series grader with the D3400 and electric start pony.  Is this 6 volt system positive or negative ground?  I couldn't find any information in the parts, operator, or service manuals.  It has a cab and I would like to keep the heater and electrical system 6 volt and maybe add some lights.  I removed the old cables and forgot to make note if the larger post was on the ground or hot cable.

Negative ground Pete

Okay, thanks Steve.

Hi, Folks.
Now I'm wondering, did Cat EVER make a positive ground electrical system on any of their machines?

Or was that a peculiarly English thing?

Just my 0.02.