No torque on front wheels in 4x4

I have a 89', that I only purchased this year, with four wheel drive. In a recent snow I shift it 4 hi and the indicator by the shifter lights up indicating that I am in four wheel drive, I even hear a change in the gears and drive. However I don't get any extra traction, I even got stuck in a small snow drift because I didn't have any weight in the rear. I don't have manually locking hubs and I can't find a fuse for automatically locking hubs. I need suggestions as how to find the problem.

i have a 95 S10 pickup with electronic 4x4 and am experiencing the same problem, press the button , ....but nothing ,NO 4x4
opinions appreciated.

I had a 84 S-10 and had this problem and it may be yours as well. Under the hood on the left side compartment by the fender is a round vacum that pulls a cable linked to the front differential. When you use the shifter it will cause the vacum to pull that cable engaging the front end. Check to make sure the vacum hose to this unit isint unplugged also check all the vacum hoses underneath the truck going in to the transfercase as well.

Hope this helps.

Bingo Rob12, yes my vacuum hose on the transfer case had worked itself loose, all hooked up and good as new.
Thank you,