Unhook the battery negative terminal. With everything off in the car, measure
DC current between the negative battery terminal and the lead you just removed.
You should measure very low DC milliamps 25+- fluctuating. That's to power
the computers. It will be higher since your battery is discharging.

Pull fuses one by one to find the guilty circuit. When the current drops to
the DC .025A +- (25 ma) you found it.
Likely you will find the problem circuit this way.

If you don't find the guilty circuit that is draining the battery after
pulling every fuse. Look for unfused items, maybe shorted alternator rectifier diodes.
If the short is in an unfused circuit then you start looking for
pinched wires, and it gets tricky.

WARNING: When measuring DC current with your multimeter:
The ammeter is connected in series with the battery and total load of the car.
Don't let anyone run the window motors or anything while you measure current since
you can damage your meter or blow a meter fuse.
Start on the highest current scale with your meter and work down to read the expected low values.

Post back with your results, Bill