I have a standard generator 12v set up with external regulator.

It appears the car is not charging

I checked battery voltage and it's around 12.5v when not running but stays similar when it is running.

I then repolarize the generator by removing wiring and fan belt and linking D+ to pos on battery and DF to neg on battery. The dynamo spins, I allow it to spin for around 3-5 seconds. Then I replace wiring and belt and try again, I still get the same voltages.

I then push the brushes towards the rotor but voltages remain the same

Is my generator knackered? Or am I missing a trick?

When I had this  it turned out to be the regulator knackered, Ive got a new one in the garage somewhere as I swapped to alternator.
You say you pushed the brushes, I would have thought if they were shot then it wouldnt have run like a motor.  They are fairly easy to check depending on how much access you have

Might be worth getting your wallet out and getting a regulator

Good luck
Dave

What revs are you at when checking the voltage........dont forget dynamos wont charge much, if at all at tickover.

I be revved the engine to check the voltage but it stays the same around 12.5v I was expecting it to jump to 14.4v or thereabouts. I then removed wiring from generator and put DF to earth and checked voltage on D+ and it goes upto about 50v so this shows generator is ok. I then changed the regulator and get the same results just stays around 12.5v

Am I missing something?

Had the same issue on my buggy before I swapped it to an alternator etc.

Yes the external regulator swap and the re-polarisation are the first things. And of course checking the state of the brushes in the dynamo too.

As it turned out in my case, it was the wire connectors within the dynamo which linked the brushes to the external terminals - wire broken and loose! And to be honest short of stripping the whole thing down was pretty much impossible to fix. So have a good close look and see if they are still attached and if not - do a complete swap.

EDIT: Sorry just re-read your issue Gary and realised its nothing to do with my post. Still, I suppose its a useful thing to check in case anyone else is reading in....