Sorry for any confusion, let me try to explain it another way...
My Multimeter positive is on battery positive. My multimeter negative is on the positive brush. I am reading Battery voltage. Which is telling me the brush (and the rotor it is touching) is grounded. If the positive brush wasn't grounded, it would give me a reading of zero. No?
sorry in the ensuing bun fight nobody addressed this question.
the answer is no!
all you are doing is connecting your multimeter to 2x seperate 12v+ supplies which will give you no reading on the meter
If you watch my video right through it will explain exactly how the charging system works however a quick explanation might help.
The stator outer brush is fed by a 12v supply when the ignition switch is turned on.
The outer stator brush feeds that 12v into the outer Rotor ring via the brush.
Once in the rotor the 12v feeds round the wire coil in the rotor until it reaches the inner rotor ring.
It is then fed out of the inner rotor ring, via the brush,into the inner stator brush holder.
The inner stator brush holder then connects directly to ground -0v on your 75 model with a black wire to the regulator and a seperate black wire to a tag on the stator body as described by gggary that basically completes the circuit.
This electrical circuit through the rotor creates a magnetic field in the rotor which when spun inside the Stator generates a AC voltage in the stator windings .
This Ac voltage is then rectified by the rectifier and regulated by the regulator . Thats a very basic description to give you an insight into how the alternator charging system works.
You need to do the 2x tests I suggested in my original post but in addition because we do not know what the previous owner (PO) has done I would suggest that you disconnect the electrical connector on the regulator and rectifier to do the tests.
If the wrong regulator rectifier has been fitted or something incorrectly wired you may need to check the fuse hasn't blown