Heated Wing Mirrors not working ?

[dt-tdi]

Hi all

Probably the wrong time of year to be diagnosing this issue but I did notice during the winter months that both my heated wing mirrors aren't working even when the rear heated screen is turned on.
Can anyone point me in the right direction to fix this problem?

I've removed the drivers side mirror because I noticed that the adhesive had come away a little causing the mirror to vibrate when driving, I've since secured it back in place using 3m adhesive pads.
I've used a multimeter to confirm continuity accross the terminals of the mirror itself.
As you can see from the pics I don't have a separate switch for the heated mirrors, so are they supposed to come on when the heated rear screen is turned on or how are they turned on?
Is there a separate fuse for the heated mirrors and if so where is it located?
Any help would be much appreciated

 

[NHN]

The middle 12 o'clock is for heated, they should be coded & they only come on at certain temps, although you can turn on the rear demister to activate, they pulse, not constant 12v, Dremel clean the contacts back to silver on the mirror glass & base pins as these lose connectivity due to the weathering.