Would like to have the mirrors heated in this cold weather. Removed the passenger glass and found the wiring nestled nicely behind the non heated glass. Put my multimeter on the wiring and turned on the engine and rear heated window (mirror switch in centre position) and there's no voltage across the contacts, should there be ? I did read somewhere that the car expects a resistance before it will supply current to the circuit but would anyone know ?
If it means anything according to the handbook if you have heated mirrors there should be a heating symbol at the bottom of the mirror control switch which mine doesn't have.

Do I need to do anything other than change the glass for heated ones and the car will then 'recognise' the glass has resistance and start working or am I doing something wrong with the switch position? The outside temperature was 6.5 degrees C, not sure if that has any effect. Is there a fuse or relay I need to add to get these working perhaps ?

If someone could advise on this I'd really appreciate it as it might be a simple fix ?