GMC C series 2002 Owner's Manual page 93

Marker and Clearance Lamps Switch
(If Equipped)
If your vehicle doesn't have a radio, the switch is
located just above the storage area. Use the switch to
operate your clearance and marker lamps. The marker
lamps are illuminated when the indicator light is on.
2-50
Your vehicle will have this
switch only if it is designed
to pull a trailer. If it has this
switch, you'll find it located
on the upper right side of
your instrument panel,
just above the radio.
The exterior lamp switches will not operate these lamps.
You can use the marker and clearance lamp switch to
manually blink the marker and clearance lamps by
simply turning it on and off.