Hey Tim, If the 4wd light is coming on while driving that would indicate that there is a fault being detected in the 4WD system. More common than not on this specific year and model it's due to a fault at one of the sensors on the transfer case unit. Without knowing the exact code it would be almost impossible to say which sensor exactly without testing them all manually.
Most people in this situation without the ability to get codes from the 4WD control unit, that don't want to use a mechanic, I recommend they go ahead and drain the transfer case, replace the 3 sensors on it, replace the the dust boot where the prop shaft meets the transfer case, then refill the unit. This is pretty much a guaranteed fix without doing any firther diagnostics, but doing it yourself will still run you up a tab of about $300 or so with the fluid.
if you need further help just let me know, be happy to assist.
If not just be sure to leave a kind rating is all.