In Reply to: Heated Mirrors? posted by Craig Homann on April 07, 2001 at 08:49:32:
If you remove the glass from the fixture ... (email if you need instructions, it is very easily done with a flat head very slim and long screwdriver) .... you will find two connectors on the back of the glass that lead to heating elements embedded into the back of the mirror.
Some cheap-skates replace these mirrors with non-heated ones to save a few bucks, so that may be the case with your passenger side mirror. Check to see.