'93 4X4 Won't engauge

Heres the deal. I have a chance to buy a '93 GMC 1500 Z-71 pretty cheap. Everything on the truck works, except the four wheel drive. It has been like this for 2 years. The owner took it to a garage and was quoted $800 to have it repaired. Supposivly it needs some sort of electrical harnesses, one for each wheel. I talked to a mechanic I know about it and he acted like this was somewhat of a common problem for these trucks, and there was a recall on the part that the harness connects to. So has anyone else seen this problem, and what is the estimated cost for parts only to fix it? Thanks in advance.

if you call the dealer with your vin # they can tell you if any recalls for your vehicle exist.