Electrical Demons

This is my first post and I'm glad to be aboard. I hope someone can give me advice on this, cause maybe its happened to you. I just bought this car and strange things are happening. I put a good strong battery in the car ( I now it was good cause I took it from my daily driver truck) and after 2 days of driving and sitting, the battery is dead. I took the alternator off and had it tested and it tests good. The battery load tested good as well. I am not that familiar with Chevys so I am lost lost as to what can be draining the battery. I checked the glove box light to make sure it was going out and it is. The car is a 87 Caprice Wagon , 305 V8 and automatic with all the electrical goodies and they all work. The Wagon has 266,000kms/164,000miles and is still pretty solid.

Check all the ground wires that you can find.

The most common wire that led to the same problem in my Caprices was typically the one that goes from the battery neg. wire to the inner fender. Check that the 10mm bolt is indeed tight and secure.