GMC 1996 Sierra Owner's Manual page 72

NOTICE:
If your key seems stuck in LOCK and you can't
turn it, be sure it is all the way in. If it is, then
turn the steering wheel left and right while you
turn the key hard. But turn the key only with
your hand. Using a tool to force it could break
the key or the ignition switch. If none of this
works, then your vehicle needs service.
Key Release Button
The ignition key cannot be
removed from the ignition
of manual transmission
vehicles unless the key
release button is used.
To remove the key
on manual transmission vehicles,
turn the key to the OFF position, then press the button
and turn the key to the LOCK position. Do not hold the
button in while turning the key to OFF. Keeping your
finger on the button, pull the key straight out.
On automatic transmission vehicles, turn the key to
LOCK and pull
it
straight out.
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