Cadillac 2013 XTS Owner's Manual page 318

2. Remove the bulb socket (1) by
turning counterclockwise and
pulling straight out of the lamp
assembly (2).
3. Pull the bulb out of the socket.
4. Install the new bulb in the bulb
socket.
5. Install the bulb socket by turning
clockwise.
1. Bulb Socket
2. Bulb
3. Lamp Assembly
To replace one of these bulbs:
1. Push the lamp assembly (3)
toward the center of the vehicle.
2. Pull the lamp assembly down to
remove.
3. Turn the bulb socket (1)
counterclockwise to remove it
from the lamp assembly (3).
4. Pull the bulb (2) straight out of
the bulb socket (1).
5. Push the replacement bulb
straight into the bulb socket and
turn the bulb socket clockwise to
install it into the lamp assembly.
6. Push the lamp assembly back
into position until the release tab
locks into place.