'04 F150 Supercrew Lariat. When the button on the dash is pressed to activate the heated mirrors, the light on the button comes on for a second and then goes out. The heating feature does not activate. Any ideas? Thanks.

 

Sounds like an open in the heating element.

Remove the door panel, and check the heated mirror circuit in the connector for resistance.

Pin #1 Dark green w/ violet stripe wire to pin #9 black wire.

If the resistance reads infinity or open, it is a mirror problem.

 

Temp sensor may be throwing it off.. wont work unless its below a certain temp outside. Same deal as AC in the winter.

 

I have exact same problem as eric. Did you ever get it figured out?