If I understand your post this is happening when the car is parked and ignition off.

A good way to find a draw on the electrical system, you may already know this. But here goes anyway, disconnect the + side of the bat. now connect a voltage meter, red lead to the + cable and the black lead to the + terminal of the bat. ignition OFF. If it reads voltage, start at the fuse box and remove each fuse and notice if you loose the draw. That should id the circuit causing the problem.

If not then, without knowing you car, the next two areas to look at and disconnect the wire one at at time, would be the alt. or the starter area.

To find a short in a wire, disconnect the wire at each end, the wire is now isolated. Set the voltage meter to OHMS connect the red lead to that wire and the black lead the cars ground, it should read open indicating the wire is good and not shorted to groung, if you read continuity ( 0 ohms ) that wire is going to ground and is not a good indication. Why? because the both ends of the wire are not connected/floating going no where and should not read or get to ground.