When I bought my '93 GC Limited a few months ago, I would get that warning when I shifted into 4WD (I have a NP242 transfer case). I figured it was a bad switch on the transfer case, and I bought a Factory Service Manual to troubleshoot it. Turns out that BOTH of the Transfer Case 4WD switch cables were plugged into the VIC, not just the one for the NP242. Simply unplugging the other connector fixed the problem and the VIC works fine now.... I guess someone had it apart at some time and figured that if there was a connector, it should be plugged in someplace.
'93 Limited, '96 Laredo (daughter's)