It does not really matters which of the field leads goes to the brush, or to which brush,
But it does affect the polarity of the dynamo,
So you can connect it in any random way and re-polarize the dynamo,
Or connect, check the polarity, and if it is not what you need,
(in this case, you get a positive earth) switch between the field wires.
(Or move the same field wire which is connected-> to the other brush.
I guess it would also change the polarity)
