Slow battery drain

Ok, so my dad's Bullitt had a problem that Ford supposedly fixed under warrenty. The service tech told me there was a wire in the trunk somewhere which was shorting out and slowly draining the battery. They fixed this problem well over a year ago... in fact I think its been about 3 years. The car is no longer under warrenty so now I get to play with it in another week or so when wrestling season is over with and I have time. I figured I'd post this on here and get a head start.

At first I thought it was his battery because it was the original battery and I needed a new one in my car last year. My car is only a year older then his so I thought that might be it. So we put in an Optima yellow top. Apparently he tried to start it today and the battery was dead again.

I know there is suppose to be a very minimal current draw on these cars to keep the memory in the ECU and for the radio but my Mustang has sat for long periods of time and still have WAY more then enough juice in it to fire up.

To get started I was wonder what fuses are manditory for the car to run both in the engine bay and under the dash ?

Also, what should the voltage at the battery be when the car has been siting and the GEM is in sleep mode ? What should the voltage be at the battery when the car has been off for a short period of time and the GEM is still awake ?

What about the voltage at the battery while the car is running ? I don't think the alternator is the problem because when he drives it every day it will start up just fine but I might as well double check just to make sure.

If anyone has any other tips for troubleshooting this problem they would be much appreciated.

Again, this is a 2001 GT Bullitt.