Easiest way to learn the system is in the AIM Assembly Instruction Manual ...it has complete wiring diagrams.
In the mean time.. buy a 12v light stick at local parts house.. unclamp NEG battery cable, clamp the wire end of the light stick to the cable and 'stick' the pointy sharp end into the battery terminal. (or clamp it with vise grips) Im guessing it lights up right away if you have a drain. Now start pulling fuses from your fuse box under the dash, one at a time, peek up to the light stick and see if its still lighted up... if so, replace that fuse and pull another one... keep going till you find a fuse that turns off the light stick... presto there is your open circuit, then using the AIM diagrams, back track the wire to its various end uses till you find a frayed wire or crimp or direct short and fix it.
I agree. Use the light bridge to close the circut between the neg. battery post and the disconnected neg. cable. If the light comes on you have what is called a key on drain. Then start pulling fuses until the light goes out and you found the circut that is causing the problem to fix. Also check to make sure your grounds are not corroded or loose. These can cause problems too.