The design of the lighted mirror has a cord sticking out the back that bends back and forth every time the door is opened and closed. Depending on how many times you open the door you may only have a few months before the cord gets a crack inside and the light won't turn on. It's a serious flaw. If you bend a wire back and forth a hundred times it will break. That's what's happening here.  I've had two of these mirrors fail on me after about 16 months of use. Sure Kohler sends a replacement part but that just buys you more time until the wire snaps again.