What does this button do? :S

[OZW116]

Sorry for the new guy question all but I can't seem to see what this button actually does...if anything...any help would be appreciated

Thanks.

[koan]

Turns heated rear window on and off. Circuit also has a time delay relay that turns heater off after some (how much?) time..

koan

[1974450SEL]

Turns off after 30 minutes according to the owner's manual.