Battery Drain-where to start

I have a 1988 Chevy Celebrity with approx 94000 miles on it. I have had battery problems twice since I got the car 8 months ago. I put in a new battery when I got it and then a new interstate battery about 4 months ago when the other one drained and wouldn't recharge. This time when it wouldn't start I pulled off the alternator, had it tested (OK) pulled the battery and jumped the car just to the cables and it started fine so no starter problem. Going to have the battery tested but chances are there is a drain on the system somewhere else since the battery is so new and higher quality. No lights were left on or anything. Is there any history of electrical shorts with Chevy cars during these years? Do you have any reccomendations of where to start diagnosing? It does have power seats, windows and locks, so maybe that is somehow creating a draw? I would appreciate any advice.

Thank You!