I wonder if someone grabbed an extra brush assy with the male lug on it & installed it on an earlier alt (in place of the "fld" brush holder with no male lug) & did not use insulating washers on the bolt to keep the brush from being grounded. This would have allowed current to come in from the blue hot wire on the other male terminal then go in/down/around the field circuit & out to the other brush & be grounded to the case right at the other brush which would have full fielded the system. If that's what happened actually that would have worked if they had put an insulating washer (might need 2) on the mini bolt that fastens that brush holder to the metal mounting nub on the alt case (which is grounded) so that that brush ain't grounded right there to the nub (case). Might check that out & might save you a trip.