The car will likely have some sort of parasitic load, since computers store memory. A better way to test is with an ammeter rather than a test light. Then you can find out how much drain you actually have. Here is a good document that explains parasitic drain and how to test for it:

http://flashoffroad.com/electrical/C...rrentdrain.pdf

 

If the alt and battery have been LOAD tested and check good, then check you ground connections.If they are dirty or can move them by hands they are to loose.If you have done ANY recent electrical work start there.How long dose it take to kill the battery?Hope this helps.