Cadillac 2010 CTS Sport Sedan Owner's Manual page 338

4. Remove the bulb socket from
the lamp housing by turning the
bulb socket one-quarter turn
counterclockwise.
5. Pull the old bulb from the lamp
housing keeping the bulb
straight as you pull it out.
6. Install a new bulb.
7. Reinstall the electrical connector
by pushing in the two plastic
clips.
8. Push the bulb socket into the
lamp housing and turn the
socket one-quarter turn
clockwise.
To replace one of these bulbs:
1. Push tab to remove the license
plate lamp.
2. Turn the license plate lamp
assembly down to remove it.
3. Turn the socket
counterclockwise and
remove it.
4. Pull the bulb straight out to
remove it.
5. Push the new bulb straight into
the socket.
6. Reverse Steps 1 through 3 to
reinstall the license plate lamp
assembly.