Our 1998 Altima needed a new alternator. Everything is fine, except overnight the new battery gets drawn down to 8 volts and the car will not start without a jump. For some reason when we test the alternator with the car off the alternator is actually drawing .4 volts. How can an alternator be drawing current when the car is off?
Welcome, Mike. I hope you kept your receipt as you likely have at least one defective diode in your new alternator. If you replace it and experience the same problem, you will want to check the wiring and connections between the positive battery terminal and the alternator BAT terminal to make sure it's not causing the diode(s) to fail. Or, if you prefer, you can check that before changing the alternator out, but that alternator will need swapped. Good luck.