Well,I'm way late to this party but;
1, Blown fuses don't make batteries go dead overnight,y'all can take that right out of the equation.
2, Things like glovebox lights,dome lights,visor lights,brake light switches and underhood lights do kill batts. overnight,always the first thing to check.
3, The alternator almost always works at Autozone,they're checking for charge,not for draw. The test for that is to remove the charge wire and see if the batt. dies.
4, You guys that install aftermarket stereos and boom boxes make sure you wire it right and strap up your wiring so it's not flopping around and getting rubbed raw.
After you have checked these conditions then break out your ammeters and start unplugging or disconnecting components until the needle drops.
