GMC SIERRA CK2 1999 Owner's Manual page 134

Armrest Storage Compartment
(If Equipped)
Your vehicle may have a center armrest storage
compartment in the front bench seat.
To open it, fold down the armrest and press the latch
handle located at the front of the armrest. Then, let the
lid pop up and swing open.
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The storage compartment has a cassette/compact disc
holder. The holder will store up to five compact disc
cases and up to six cassette tape cases.
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