Question re rearview mirror

Just moved to a CPO 2013 TL from a 2005 RL. The new car is immaculate, but I do have a question about auto-dimming. On my RL there was a small button btw the indicator light and the sensor on the mirror itself. On the TL there is no button and I'm not sure that it is actually auto dimming. The indicator light is not lit, even at night. Is there some other control to turn on auto dimming?

Thanks.