Cadillac 2013 Caddilac CTS Owner's Manual page 336

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.
To replace one of these bulbs:
1. Open the liftgate. See
.
2. Push the left end of the lamp
assembly toward the right.
3. Turn the lamp assembly down to
remove it from the liftgate.
4. Turn the bulb socket (1)
counterclockwise to remove it
from the lamp assembly (3).
5. Pull the bulb (2) straight out of
the bulb socket.
6. Push the replacement bulb
straight into the bulb socket and
turn the bulb socket clockwise to
install it into the lamp assembly.
7. Turn the lamp assembly into the
liftgate engaging the clip side
first.