GSXR's method IS the fastest way to solve a short circuit issue. If it's less than a 10 amp draw you can connect a DVOM between the positive cable and the positive terminal of the battery. With the meter connected, then begin pulling fuses (one at a time) to find the suspect circuit. Usually, it's something simple once you find the suspect circuit. One time on an american car, I found the seat bolted through a wire to the floorboard. Another time, I found a broken tail light bulb where the filaments had crossed. I'm not saying these are you issues, but only pointing out it's usually a simple fix, once you find the culprit.

Short of doing that (pun intended), you could try - as GSXR said - to remove the fuses one at a time while connecting the battery and watching for this loud spark you described. If the spark doesn't occur, you have found the suspect circuit.

Also, since it's a battery drain with the engine off, I would be only suspect of the circuits that operate without the key. i.e. the seat switch/motor/wires that operate with the door open, etc. Again, probably not the seat or switch, but I think you may be getting the idea...

Good luck!

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