Subaru 2004 Impreza Owner's Manual page 178

Semi-automatic climate control system
To turn on the defogger, push the switch. To turn it off,
push the switch again.
The indicator light located on the switch lights up while
the rear window defogger is operating.
NOTE
If your vehicle is equipped with the outside mirror
defogger, the outside mirror defogger operates
while the rear window defogger is operating.
" Do not use sharp instruments or window
Instruments and controls
cleaner containing abrasives to clean the inner
surface of the rear window. They may damage
the conductors printed on the window.
" To prevent the battery from being dis-
charged, do not operate the defogger continu-
ously for any longer than necessary.
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