Global Machinery Company Sierra 1999 - Manual (Page 128)

yellow blue
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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.
Electrochromic Inside Rearview Mirror
with Compass (If Equipped)
Your vehicle may have an electrochromic inside
rearview mirror.
When on, an electrochromic mirror automatically dims
to the proper level to minimize glare from lights behind
you after dark.
The mirror also includes an eight - point compass display
in the upper right corner of the mirror face. When on, the
compass automatically calibrates as the vehicle is driven.