A parasitic draw test is pretty easy to do. With a digital meter, switch to the amps side. Disconnect the positive cable. Connect your meter's leads in line between the now loose positive cable and the other to the battery. Make sure you don't don't do anything that would pull a high amp draw (like turning the key to crank) or you'll blow the fuse in your meter. The whole key to this test is watching what your draw is when every thing is off.
Take a baseline reading with the doors shut. Normally with the doors shut and key off you shouldn't have more than 50 milliamps. Chances are if you do have a draw it will be higher than that. Open the door and then pull the fuse for the dome lights or use some duct tape on the door jamb switch to keep it closed. Then start pulling one fuse at a time, each time checking the meter to see if your value dropped or stayed the same. Go through the rest of the fuses until you find one or more that drop the value to an acceptable value. Once you find it you can then figure out why it's staying on and address it.
I was helping a buddy run this test on a 55 Nomad at the Nomad convention last year. It had stock wiring so it had less circuits than any K5 and once we pulled them all it still was pulling 5 amps. We then pulled the hot lead to the alternator, still pulling. We went to the horn relay (which is a main power distribution point on a '55), disconnected it and the draw went down to under 10 milliamps. So keep that in mind, if all the fuses are pulled and your draw doesn't drop you then need to go back to items that have access to constant power. Starter, alternator and a digital radio memory circuit are the first targets to shoot for. A wiring diagram is an excellent item to have so you can pinpoint other constant hot circuits.
Just take your time and you'll find it.