GMC 2000 Sierra - Manual (Page 132)

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position, the dome lamps will remain off when the doors
are open. To return the lamps to automatic operation,
press the button again and return it to the “out” position.
With the button in this position, the dome lamps will
come on when you open a door.
Cargo Lamp
Press the button to turn the
cargo lamp on. Press the
button again to turn it off.
A message in the instrument
cluster will come on and
display CARGO LAMP ON
when the cargo lamp is
turned on and the ignition
key is turned to RUN.
Battery Run-Down Protection
This feature shuts off the dome, reading, glove box,
cargo and underhood lamps if they are left on for more
than 40 minutes when the ignition is off. This will keep
your battery from running down.
Mirrors
Inside Day/Night Rearview Mirror
Pull the tab under the mirror toward you to reduce glare
from headlamps behind you after dark. Push the tab
away from you for normal daytime operation.