Good morning
I have 2013 TL I noticed last several day my mirrors are not defrosting. The rear window defrost works. I thought mirror defrost is together with rear window defrost?
any ideas?

 

They are not together, all 3 elements work separately from a separate power supply, the only thing that connects them is power management and a B-CAN. To begin, remove the driver's door panel and check the resistance between the 1st orange wire of the master switch and ground (car body)

 

I just replaced the mirror and it worked for me.

I have used the heated mirrors in spring/summer sparingly when it's raining, It will clear up the mirror nicely. I have also Rainx'ed my windows as well. I would turn it off manually to not push the system too much.