Electrical problem help please?

[Gpaw44]

What might be causing my battery in my 86 GMC 305 to be drained overnight. I got a new battery yesterday and by morning it would start. Any suggestions would greatly be appreciated as what might be wrong or where/how I start looking for what is wrong!

 

[73c20jim]

Did this also happen to the old battery???

 

[Gpaw44]

Yes. I put my meter on the new battery earlier in the day and I could watch it drop. I charge the battery up and disconnected the alternator and it is still holding a charge. It was getting late so tomorrow I am going to plug the alternator back up and see if my meter starts dropping. I have a howling noise while running that I didn't have before, maybe I need a new alternator. It has been repaired before.

 

[Charlie]

Yes, possibly alternator. Put meter on battery while running. Should be getting around 14.0 to 14.5V.