Does anyone know why one of my heated Morris will not work. I don't know if there is a heating element that you can replace or what.

 

Gently pry the mirror off from the control mount. There are wires behind it. Check the voltage with a multi-meter to make sure you're getting power. If so, the mirror itself needs replaced (about $25 or so) as the element is behind the mirror. If you are not getting power, there's a short somewhere in the mirror or door.