2003 Honda Civic rear defrost button

I noticed that my rear defrost button is turning off after approx 20 minutes, and the normal backlight isn't lit when I have my car lights on in the evening, whereas the A/C light next to it is lit. I'm not sure what is causing this and if this is an easy fix, since the defrost button does actually come on, but for some reason it is turning itself off. a few weeks ago I had a new car stereo installed, and these buttons are right below that area. is it possible that the wiring may have been pulled loose when the stereo was installed? are all of these areas open to each other, or would these buttons be separated from the stereo area? thanks.
tanya