SYSTEM IS DRAWING FULL BATTERY LOAD IN THE OFF POSITION.
NARROWED DOWN TO 3-WIRE FEED TO THE IGNITION SWITCH(LOCATED
UNDER FUSE PANEL).

Do you mean 12 Volts or enough Amperage to burn stuff? There are items that get power all the time from circuit #30. The key is how many Amps they are pulling. If the three wires are big red ones, you may have found the feed to circuit #30 from the battery.What are the symptoms? Do you have a meter that can measure Amps?
Randy D.

THE SYSTEM IS DRAWING 5.22 AMPS.

OKAY. (Hit the caps lock button again, no need to "YELL"....we can see it just fine.)So you have 5.22 Amps of drain...
Step #1: Be sure to hold the negative terminal against the battery for 30 seconds or so until the lock pump cycles. The lock pump will run anytime the battery is disconnected and reconnected.
Step #2Though you probably already did)Pull the fuses one at a time to try and isolate the circuit involved. If you find something here you have to unplug the components on the affected circuit to isolate it.
Step #3: Having found nothing in step #2, look at non-fused consumers (alternator, glow plug relay, alarm system).
That's about all I can guess from what little I know.
Randy D.