I just installed a new battery in my 51 super & in draining over night. No lights were left on and all the accessories were off. Does anyone know what could be drawling power from it?

Just to be clear, you're talking about a 1951 Buick Super, right? I believe those still had a 6 volt electrical system so the new battery was a 6V battery right, or had the electrical system been switched over to 12V? A little more info might help.

1. Remove the negative cable from the battery.
2. Connect a multi meter set to read milliamps between the negative terminal of the battery and the end of the disconnected negative battery cable.
3. On initial contact, the car'* computer systems wake up, and there will be an amperage reading. Wait for that initial reading to drop as the systems go back to sleep. (this likely does not apply to your vehicle)
4. If the ammeter is reading over 25 to 50 milliamps, something is using too much battery power.
5. Remove and replace each and every fuse and relay, one at a time, and note the amperage reading each time you pull a fuse.
6. The fuse that reduces the drain will point you to the culprit.

If you are sure there were no lights left on, I would suspect the voltage regulator. I've had this happen to me a few times over the years.

Charge up the battery to a full charge. After a few hours of the car just sitting, lay your hand on the regulator. If it feels warm/hot, the regulator is pulling voltage from the battery.

Joel

I'll give it a shot, thanks JOel

Yes its a 51 super and it does still have a 6 volt system. Thanks for the reply.

Welke, that was a good call by Joel to check your voltage regulator, if indeed it seems to be the problem, there may be an easy fix. I believe those old time voltage regulators had a set of points to interrupt current flow from the generator to the battery when it was fully charged or when the vehicle was not in use. Said points may be stuck or may need to be cleaned/filed. Also those old voltage regulators were adjustable, many old-timers would run a 8V battery that would spin the starter a little faster especially in cold weather and the 8V wasn't enough to burn out 6V bulbs. Of course the voltage regulator needed to be adjusted to keep the battery charged up. I believe Tractor Supply Co. still sells 8V batteries if that'* a route you would ever want to pursue.

Thank you sir! I'm going to give it a shot.