2013 Toyota Tundra CrewMax Owners Manual - Page 278
2013 Toyota Tundra CrewMax Manual
Page 278 highlights
3-1. Using the air conditioning system and defogger Vehicles with a manual air conditioning system On/off Press the button to turn on the outside rear view mirror defoggers. The indicator will come on. The defoggers will automatically turn off after about 15 minutes. Pressing the button again also turns the defoggers off.