Cadillac 2010 DTS Owner's Manual page 194

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.
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The light sensor is located
on the inside of the
vehicle in front of the
inside rearview mirror.
This feature activates the headlamps and parking lamps
after the windshield wipers are turned on and have
completed eight wipe cycles within four minutes.
When the ignition is turned to LOCK/OFF, the
wiper-activated headlamps immediately turn off.
The wiper-activated headlamps also turn off if the
windshield wipers are 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.