It reads like that 50amp fuse powers the Cab Fuse box, I/P = instrument panel
Fuse box in the engine bay is called Battery Junction box, it feeds power to the Cab Fuse box.
Cab fuse box feeds power to most of the cab devices
So leave that 50amp fuse in place then move to Cab and start pulling fuse and watch the test light.
Just as a heads up, batteries can self drain, have you disconnected battery over night and does it still start engine the next morning?
1997 Ranger should have a Battery Saver Relay, it is behind the Radio.
This relay prevents most shorts, or left on lights, from draining the battery.
Battery Saver Relay doesn't shut down power when key is turned off, it waits approx. 20 to 30 min. after key is out and doors are closed.
You really need an AMP meter connected like test light is now.
Because battery is ALWAYS being drained, just a low amp drain for radio pre-sets, computer memory, and wireless key fob detection.
Your bright test light means there is a larger drain, but GEM module will be on and other electrics until Battery Saver Relay cuts power to them.
So I would leave key out close the doors and wait 30mins to see if test light dims, if it doesn't then I would look at Battery Saver Relay as being bad first.
With amp meter hooked up a working system will draw .03-.07 amps after battery saver relay cuts power.
This thread has 1997 fuse box layouts: Ranger: the heater fan is not working..blower works
Fuse 28 GEM system seems to also be battery saver circuit, try pulling it out and see what test light does