1999 Chevy Silverado 4X4. The Service 4WD light is on most of the time....

[Brian]

...Does anyone have any suggestions? I have checked all of the connections and all look good, no corrosion or broken wires that I can find. Details on the truck; 1999 Chevy Silverado Z71 4X4, automatic transmission, 5.3L V-8. As I stated the Service 4WD light is on most of the time and the 4WD is not working. I live in Michigan and vehicle is driven daily, no unusual noises so I don't think it is a mechanical problem.
Any suggestions as to where to look would be greatly appreciated.