GMC 2000 Sierra 1500 Pickup Owner's Manual page 29

Lap-Shoulder Belt
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The driver has a lap shoulder belt. Here's how to wear
it properly.
1. Close and lock the door.
2. Adjust the seat (to see how, see "Seats" in the Index)
so you can sit up straight.
3. Pick up the latch plate and pull the belt across you.
Don't let it get twisted.
The shoulder belt may lock if you pull the belt across
you very quickly. If this happens, let the belt go back
slightly to unlock it. Then pull the belt across you
more slowly.
4. Push the latch plate into the buckle until it clicks.
Pull up on the latch plate to make sure it is secure.
If the belt isn't long enough, see "Safety Belt
Extender" at the end of this section.
Make sure the release button on the buckle is
positioned so you would be able to unbuckle the
safety belt quickly if you ever had to.
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