What would cause my 2008 F150 radio lights to fade away?

I have a 2008 Ford F150 and the lights on the radio will stay on like normal sometimes and other times the lights are barely able to be seen or not at all. I have not noticed any problems with any of the other electronics except the cruise control does not work. I don't think that would have anything to do with it though. What can I check or what would cause the lights to fade in and out? My Dad swears that when he taps on the plastic cover that the lights sometimes kick back on but I can never get that to work.

If you turn on your headlights in the daytime the dash lights will come on and the radio lights fade. You won't notice the dash lights on in the daytime but the radio is definitely noticeable. If you change the dash light intensity it often changes the the radio light intensity as well. Make sure you understand this functionality (see owers guide for details.).