Chevrolet Repair: 88 Chevy Silverado 4x4 issue, fuse box, chevy silverado

Question
My daughters 1988 Silverado 1500 has 4x4 capabilities with the  floor mounted shifter. We were told at the time she got it that  the 4x4 was inoperable and not to use it and that it needed a $200.00 part to make it work again. Upon inspecting it, we find that the 4x4 does engage when the shifter is moved into both hi and low positions but it appears to not actually be rotating the proper number of wheels. We suspect that the gear box is operable and the issue lies either in a sensor or cellenoid on top of the gearbox that relays a message to the system telling it which tires should be in rotation or something somewhere in the differential. The differential is not turnable by hand when locked into the 4x4 position -vs- being movable when in the 2wd position. We are trying to determine the necessary "$200.00 part" that is needed to make the 4x4 fully operational, however the person who knew what this part was has since passed away. We are hoping for a starting point to narrow this down before taking it in for repairs to try and avoid being "misinformed" or overcharged for unnecessary parts and labour.

Any ideas?

Thanks :)

Answer
There is a front axle actuator that goes bad a lot on t he truck. I would start there. You can check this by jacking the front wheels up and rotating the front wheels while it is in 4 wheel drive with the ignition key in the on position. You should not be able to turn the wheels, if you can replace the actuator. Be sure to check the 4wd fuse in the fuse box too.

Hope this helps

Have a Great Day          Mark