[aj.lec]

I agree with Ian
The second set of brushes is unusual ,normally only have the one pair
Of these pair ,one brush will be grounded to the case
the other will connect to the A terminal
also coming off the A terminal is one side of the field wiring
Off the F terminal will be the other side of the field wiring

Bearing in mind these are not a permanent magnet generator you do require an excitation voltage which is supplied from the regulator to create an induced voltage
The wiring of which is BAT terminal to the battery via the Ammeter
GEN terminal to the A terminal of the generator
And F to F on generator

So bearing this in mind if the generator was indeed reconditioned correctly the most likely cause of your grief usually comes from stuck or open points on your regulator ,ineffective insulating blocks at connection points or an open circuited ammeter