a better method is to use a multimeter, a cheap digital will do the trick.
as previously stated, make sure everything is off, doors closed etc etc
disconnect the -ve terminal
now with the DMM set to DC amps range usually 10A, if you're unfamiliar with how to read amp draw and the multimeter has an auto range function, switch it off so it only reads amps and not milliamps etc. With the leads plugged into the correct sockets (DO NOT place the probes across the battery in amps range), place 1 probe on the -ve battery terminal and the other probe to the now disconnected -ve terminal for the car, check how much is being drawn.
Ignore the initial spike as it's most likely the ecu and/or radio drawing an initial charge for their memory, which is also what can cause the initial sparking when you reconnect a battery, wait a few seconds and then read how much current is being drawn.
Also obviously don't try to start the car with the dmm in place, you'll blow it's internal fuse.
If it's an excessive amount of an amp or more then you'll have to find the culprit.
The easiest would be to connect the battery back up normally and take the dmm to the fuse box.
1 by 1 remove a fuse and place the probes on either terminal until you find which circuit the current draw is on, from there it's a matter of tracking down what is causing it, most likely you'll have the door open and the interior light will be on, if you get a reading depress the door switch to turn the light off, if the reading goes away then move onto another fuse, at least you should now have a direction to look and not just blindly look at globes, faulty switches etc.