2001 Ford Ranger on-the-fly 4x4

My son’s 2001 Ford Ranger’s on-the-fly 4x4 decided to stop working as he was driving through a snowstorm on Christmas Eve, which made for a really dicey drive. When he went to switch it on, nothing happened. Usually he can hear a click, and feel it kick in, and the 4x4 indicator light comes on. Since then it won’t come on. We checked the fuses and none of them seem to be bad, although we’re going to replace the ones related to the 4x4 just in case. Any other ideas what it could be?

Changed the fuses but that didn’t do any good. My son headed out for the drive home across the Rockies, hopefully with sufficient time to make it before the next storm hits. He’ll take it to a garage, but would like to have a general idea of what the fix might be so he doesn’t end up having a bunch of unrelated work done.

Manual shift-on-the-fly or electronic shift-on-the-fly?

The fault MAY be with the switch itself or possibly a fault with the shift control module at the transfer case.