First of all I want to wish you a quick recovery.
If you are already plying with bike, it is a good sign..
I had an 8 hours long major surgery, and after recovering,
I found some things missing that I just do not remember.
Most of it came back as time passes.
Regarding the voltage measuring-
Just to make sure-
You did it on the DC position, right? not the AC.
Yes Noam, I made the checks on the DC scale. Checked again today but I still have the same problem. Further fiddling around with the dynamo suggests that the fault might lie in the brushes, in that applying pressure on the them while it was running made the scale drop to zero. Which was just the opposite of what I expected ! :-) The brushes have plenty of length to them so I wasn't expecting anything faulty there - assuming it is.
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)