Chevrolet 1999 Silverado 1500 Pickup Owner's Manual page 77

There are several ways to lock and unlock your vehicle.
You can use the keyless entry system (if equipped).
You can also use your key.
Use only the key or the keyless entry transmitter if your
vehicle is equipped with the content theft
system and the system is on.
-
deterrent
From the inside, to lock the
door, slide the lever
rearward.
To unlock the door, slide the
lever forward.
Power Door Locks (If Equipped)
Press the recessed side of the switch marked "U" to
unlock all the doors at once.
Press the top of the switch to unlock all the doors at once.
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If your vehicle has this
power door lock switch,
press the raised side of the
switch, marked "L" on
either front door to lock
all the doors at once.
If your vehicle has this
power door lock switch,
press the bottom of the
switch on either front door
to lock all the doors at once.
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