It appears that it is normal for the mirror heaters to run all the time. This seems unusual to me - my Maxima had a separate switch. I have felt the mirrors and they are quite warm - especially during our 100 degree summer days. Is this correct?
They are working normal. The side mirrors must be heated in order for the self cleaning feature to work. When water touchs the mirrors it quickly flattens and drains off of the mirror glass. Many of the 2001 Lexus models will have the same feature.