GMC C-Series 2001 Owner's Manual page 98

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.