pull the blue/green field wire connectors off of the alt field terminals and ohm the male terminals (the alt internal field circuit). then ohm each one to the alt case. visual on the brushes/brush holders for any (improper) continuity to alt case that you can see. pull the brushes/brush holders & visual for anything that dont look right such as something touching that should not be touching & when replacing them they wear at an angle so restore that clocking. You might also sub in another alt for a quick test (I have a dozen I am tripping over) or take it in to your parts house & have them spin it. borrow another good/fully charged battery & sub it in for a quick test. pull all blue/green field wires/connectors off & with jumper wires with small alligator clips (fab em up they will come in handy in the future) jump 12V to one field terminal and 12V to the top nub terminal in the reg triangle with it facing up like a pyramid as some are not and run a jumper from the side reg nub terminal to the other alt field terminal (no voltage,just connect those 2 to each other, you are duplicating the green wire alt to reg field circuit) & run it at a fast idle & see what you get for voltage at the alt "batt" stud terminal and at the battery posts. Only do each running test for ~4 seconds just long enough to read your meter as this high of pressure is extremely damaging to the system & have the lights/radio etc OFF. I'd do the battery first (easy to do) then the alt then the jumpers. Holler back when you can. WAG-the alt (part time loose or dead shorted connection). EDIT confirm there is no draw with everything shut off (pull a batt cable off of its post at midnight & should be no spark (assuming no clock or LED indicator light on a stereo face etc that is on all the time) & this is with eng OFF, all lights everything off (no spark=no draw)