Chevrolet 2003 Astro Owner's Manual page 138

The exterior lamp control has three positions:
0
(Off): Turning the control to this position turns off
all lamps except the Daytime Running Lamps (DRL).
%:
(Parking Lamps): Turning the control to this
position turns on the parking lamps, together with the
following:
Sidemarker Lamps
0
Taillamps
License Plate Lamps
0
Instrument Panel Lights
Ashtray Lamp
-g-
(Headlamps): Turning the control to this position
turns on the headlamps, together with the previously
listed lamps and lights.
Automatic Headlamp System
When it is dark enough outside, your automatic
headlamp system will turn on your headlamps at the
normal brightness along with other lamps such as
the taillamps, sidemarker, parking lamps and the
instrument panel lights. The radio lights will also dim.
Your vehicle is equipped with a light sensor on the top of
the instrument panel in the defroster grille. Be sure it
is not covered, or the system will be on whenever
the ignition is on.
The system may also turn on your headlamps when
driving through a parking garage, heavy overcast
weather or a tunnel. This is normal.
There is a delay in the transition between the daytime and
nighttime operation of the Daytime Running Lamps (DRL)
and the automatic headlamp systems so that driving
under bridges or bright overhead street lights does not
affect the system. The DRL and automatic headlamp
system will only be affected when the light sensor sees a
change in lighting lasting longer than the delay.
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