GMC C series 2002 Owner's Manual page 97

Auxiliary Power Jacks (If Equipped)
-
These jacks provide 12 volt power so you can
operate things such as a citizen's band (CB) radio
or a cellular phone.
You'll see positive (red) and negative (black) outlets.
-
They have a 20 amp fuse that is common with the
cigarette lighter. Don't use the cigarette lighter when
you're using a power jack because it may overload the
circuit and blow the fuse.
2-54
If your vehicle has these
power jacks, you'll find
them in the ashtray.
NOTICE:
Whether or not your vehicle has the power
outlets, don't plug in FM communications gear
at the ashtray area. FM equipment creates high
heat, and over time the area could get so hot
that wires could be damaged or a fire could
even break out.