Service 4WD light on?

Yes, you can drive it with the light on, it just means the 4wd operation is not working. There are two fuses to check # 12 in the under-hood fuse panel and # 19 in the fuse panel under the dash on the left side. If they are okay it sounds like the switch has gone bad, here are the transfer case wiring diagrams so you can see how the system works. Also, you can do a CAN scan which will go over the entire truck, which is easy to do, you can get a CAN scanner (Controller Area Network) from Amazon for about $36.00.

Here is a video to show you how:

https://youtu.be/u-4syLc-ifQ

Here is a scanner link:

https://amzn.to/3eCqWWw

Check out the images (below). Please let us know what happens.