key doesn't turn car off

I feel I've had this problem before but for the life of me, I cant remember what I did to fix it. The car is a 71 Duster, 318, points ignition. The engine will turn on with the key but not off. I have found there to be a draw at the battery, the alternator being the culprit. I disconnect the alternator, no draw. When the car is running, it will turn off if I unplug one of the field wires from the alternator or disconnect the battery. Enough info? Whats up?