battery goes dead overnight

I have a 2001 mountaineer aka explorer which the battery goes dead every 2 weeks. Sometimes overnight . I have had the alternator checked and it was okay. and i have replaced the diehard battery twice and it still does it. I know it is electrical but were do I start looking.

Any "aftermarket" electrical work such as stereo or amp work done? what about non-factory alarm?

start at the batery terminals and follow them to check for any posible damage to the wires(rust, cuts etc). if u have this problem it is probably a coraded wire someplace. also like the other guy said any "DYI" or aftermarket wiring could be faulty.......good luck

Like was mentioned, check any aftermarket accessories. Check for interior lights left on. Do all electrical systems work? Someone hasn't disconnected something that wouldn't shut off and left the relay energized?

Next, you need to check for a draw. If you find it's excessive (which you probably will), start pulling fuses until it goes away. Now you know what circuit it's on.