Hyundai Repair: Electrical Issue, 5th gear, dash board

Question
My radio works when it wants to.  When car is warmed up the rear defrost will not work if my foot is on the accelerator.  Brake light and battery light on dash board flicker when I am in 4th or 5th gear and my foot is on the accelerator,; if I remove foot no flickering.  Shop wants $92 to diagnose, unless it is complicated then the price will go up.  How can I fix myself?

Answer
If your battery and brake lamps are coming on, your alternator is not charging.  If the belt is present and tight, you should replace the alternator.  This should solve all the issues with the possible exception of the radio, which I suspect is a problem within the radio itself.