4 wheel drive not working on 1993 Toyota T100

I'm trying to get my four wheel drive working on my 1993 Toyota T100.
When you shift it into four wheel drive it down shifts so it goes
slower so if feels like it's engaging but when you get stuck the front
tires don't spin. I heard that it can be the hoses that go to the
differential but I looked at these and they look good. Also, the four
wheel drive light on the dash does not light up when it's in four wheel
drive. I have heard from Toyota that the hubs are always locked on the
T100's because I originally thought that they were autolockers and
weren't locking. If anyone has any idea's of anything I can try to do
to figure it out please let me know. Any help would be appreciated.

Thanks

I forgot to also say that the front differential is ADD (Automatic
Disconnecting Differential).
Thanks