Ford Repair: Ford Aerostar battery draining, ford aerostar, volt amp

Question
Hi.  I have a 91 Ford Aerostar that keeps draining the battery everytime I leave the car alone for about an hour.  I had the battery & alternator checked at autozone, but they said it was fine.  I also had all the fuses checked.  This started after I had the serpentine belt changed.  I don't know if that has anything to do with it.  I was hoping you can help me pin point this.  thanks.

Answer
Hello and thanks for the question...I'll try to help.
 What you need to do is get a volt/amp meter. Disconnect the positive side of the battery, and then connect the meter in between the battery cable end and battery terminal. Make sure you have the meter ON Amps and set at a high Amp reading at first. Then lower it until it won't show a reading, then set it back to the scale just above that. After this is done, start pulling fuses, one at a time and look at the meter. When the Amps drop to below .o3 Amp, you know what circuit the draw is on. You can then trace the problem to the source.
Also, while doing this make sure that the under hood light is either unplugged or out, and also DO NOT have the keys in the ignition.
Hope this helps,
Erik