Transfer Case Shifting

[TR4Petty]

My '91 4x4 V6 Dakota has developed a problem. When I shift from 2H to 4H lately, it doesn't always engage the front end. The 4WD light comes on but the front end is not hooked up. If I keep going back and forth between 2H and 4H, it will eventually catch. It has snowed a couple of times here lately and that's how I found out. I would put it in 4H but would start spinning just the rear wheels. Only after moving the lever back and forth from 2H to 4H while pulling forward and backing up did it finally catch the front wheels. The 4WD light was on the whole time though. Any ideas what to look for?