4 wheel drive does not engage

I have a 1992 Explorer 4X4 with 127000 miles. When I pushed the button to engage the 4 wheel drive nothing happened. I also noticed that the Low Range light is not on. I've always thouight that it worked until I got stuck in the snow and switched it on. It didn't seem to make any difference, the rear wheels just spun. Would appreciate any help.
Thanks, Retired.

Here is what I did to my wifes 93. On the rear of the transfer case you'll see a weight looking thing remove it. Behind that you will see a circle that is held on with a triangular bracket with 3 torx bolts (I forget the size its been a while) Mark the position of the plate under the triangle remove the triangle....You might want to get a pick and clean the holes of the torx bolts. Carefully remove the circle and look at the back of it you will see some copper contact points on it. Lightly sand the contacts you may wand to give them a little bend up. Inside the transfer case where you took the circle out you will see a wheel that looks like a circuit board,, lightly sand it also. Clean the contacts and the wheel by spraying a small amount of carb cleaner on a rag and wiping the parts be carefull not to bend the contacts. I don't know if this is what your problem is but I was told to do it on my wifes and it worked for 3 years till she traded it in.

Hi retired I have a 91 Explorer XLT with 147K on it. First check all fuses. A comon problem I here is the transfer case actuator motor going bad. The brushes inside this electric motor are usualy the cause. I removed mine today and found the armatute magnets inside had broke into about 30-40 different pieces. A service technician can determine if the switch, control module or this device is at fault by reading a red "LED" light on the module mounted in the compartment where the jack is stored in the rear cargo area. They can also check the electrical conections with an ohmeter and determine if the actuator motor is bad. "Good Luck!"

Thanks for the advise. I had the car checked out at a shop that I have some confidence in and was told that it is indeed the actuator motor, ($400 for the motor).

Retired