1991 4X4 indicator light doesn't work

I have a 1991 4X4 Explorer with a 5 speed manual transmission 4.0 liter. The 4 wheel high indicator light no longer illuminates when you press the button. The Transfer case engages, and if you activate the 4 low it also engages and the 4 low light will illuminate, but the 4 high is still out.

I have changed out the 4 wheel drive switch with one that I know works and also the 4 wheel electric motor on the transfer case. As the equipment still provides the 4 wheel drive capability it’s a pain to determine if the system is still engaged when not needed.

Any help would be greatly appreciated.