Q&A

 Master

It could quite possibly be the security/alarm system. You may have some sort of battery draw that needs to be isolated and eliminated. You would need an amp meter disconnect one cable of the battery put your Amp meter in series with the battery cable that has been removed. Note the draw say for example 15 Amps, with the keys out of the ignition, doors closed driver's window down, start removing the fuse links and fuses one at a time until the voltage draw goes away to zero (or near zero about .02 to .05 Amps is about normal for a modern vehicle with a clock, stereo and other things that need "keep alive memory"). It is that circuit that is causing the electrical draw, then look at a wiring diagram, see what electrical consumers are on that circuit and start to isolate each circuit to see which is the culprit. Modern cars have lots of computers and electronics that need constant battery even with the key off so parasitic draw of .2 Amps may be normal sometimes things stay "live for a minute or two afer the door is closed so wait and look at the draw after a minute or two.
You will need a good wiring diagram and amp meter or better yet an inductive amp meter and start disconnecting fuses to see when the "load" goes away. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online