1995 GMC Jimmy 4X4 not going in, lights up but not engaging

Hi billymac here there is a couple of things that could cause this. First on the side of the transfer case you will see a small motor remove this from transfer case disconnect plug take apart you will find rust inside clean and lube with lith grease. Reinstall. Prob # 2 possibly the transfer case is engageing, but the front axle is not locking. If so there is another motor on the front axle. This is normally the prob. FIRST raise rear axle off the ground. Start vehicle put in gear let it idle. Look under the driver side see if front shaft turns when in four wheel. If yes axle motor is the prob if not transfer motor. Be sure you block front wheels while running in gear. Mostly be very careful. Hope this helps. Billymac