i would think it has to be in the black wire from the brush to the Rectifier............can't test volts on an earth wire..........have to continuity test.......Continuity test the black wire from the brush to the connecton........If that checks then plug the rectifier in and test from the brush to the rectifier.........This will show if the Earth wire has a break in it...........is the brush grounding properly
Has the connector, on the stator side, been thoroughly examined for corrosion or a damaged connection? May need to remove the pins.
5twins posted the manual description, (with pics), testing resistance to the brush in post no #59........It talks about resistance.........Testing resistance is continuity testing.. Resistance is when there is a problem in the circuit and it shows up on the meter as a number. The higher the number, the more resistance...............No resistance = full voltage getting through......some resistance = some volts getting through, could be corrosion or a loose/intermittent connection........Full resistance = no voltage getting through, broken wire or connection