99 4wd service

I had a pretty open ended question about my "service 4wd." This has started to show up while I am driving but I can find anything wrong, the 4wd works great and always have. I have noticed the switch for my 4wd/2hi going off and on, as if I needed to change it? They do not switch back and forth among each other but if I have it just in 2hi the light turns off and on. I am not sure why else it would come on, has this happened to anyone else and if it has what was the problem. I appreciate the comments, thanks.

replace the switch, thats all it is.