Hook up a multimeter between the battery's ground cable and the ground post on the actual battery. Set the meter to amps and make sure the cable is in the correct location, mine is separate from the volt/ohm post. Also, ensure the fuse is good inside of the meter, they are usual 10 amp glass tube fuses. Now on to the testing. Ensure all of your doors are closed, lights off, radio off, etc. Nothing should be on that draws power! Note the reading on the meter. If it is under .035 amps, you are ok. If it is over, you need to start pulling fuses and isolating circuits. Since you are suspect of the amp, I would recommend starting by unplugging the harness going to it. If that brings your reading into an acceptable amount, have a beer. If it doesn't, you need to continue your search for the draw. I would recommend pulling the radio fuse next. Remember, you can't do this with doors open etc! You may have to pull the fuse or somehow disconnect the circuit for the door if it has to be open. You will also have to give time for the computers to go to sleep, this can take several minutes or should kill them as soon as you disconnect the battery then hook up the meter.
http://flashoffroad.com/electrical/B...teryDrain.html
This link should help if you don't completely understand my explanation.