Testing 12V generator output

[russcc]

The 8RT in the roadster has an original 6V generator housing converted to 12V. Where do you measure output of the generator. There are three terminals. There is a large one at the back, which I assume is Armature, and two on the side, the one on the top is marked F for field and the one below that is marked G for ground which I grounded to the regulator. Thank you.