Cadillac 2011 STS Owner's Manual page 217

The light sensor is located on the inside of the vehicle
at the back of the rearview mirror.
Clean the light sensor window, periodically, using glass
cleaner on a soft cloth. Gently wipe the sensor window.
Do not spray glass cleaner directly on the surface of the
sensor window.
This feature activates the headlamps and parking lamps
after the windshield wipers have been in use for about
six seconds. For this feature to work, automatic lighting
must be enabled. See Headlamps on page 4 27 for
additional information.
When the ignition is turned off, the wiper-activated
headlamps will immediately turn off. They will also turn
off if the windshield wiper control is turned off.
A warning chime will sound if the exterior lamp control
is left on in either the headlamp or parking lamp position
and the driver's door is opened with the ignition off. See
Lights On Reminder on page 4 67 for additional
information.
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