I was thinking we were dealing with a '70 up style alt with 2 male field terminals? If so that is a closed loop field circuit in the alt with the 2 male terminals being the ends of that loop & it cannot have continuity to ground. If it has 1 field terminal (69 & earlier type) then that male terminal will have continuity to ground since the other "grn" brush is grounded (there will be some total resistance from the male terminal down & in/around the circuit then out to the case with the "grn" brush being grounded to the case with you haveing the ohmeter leads on the male terminal and the case.