GMC 2003 Safari Owner's Manual page 26

3. Pick up the latch plate and pull the belt across you.
3. 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 on page 1-34.
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.
Don't let it get twisted.
The lap part of the belt should be worn low and snug on
the hips, just touching the thighs. In a crash, this applies
force to the strong pelvic bones. And you'd be less likely
to slide under the lap belt. If you slid under it, the belt
would apply force at your abdomen. This could cause
serious or even fatal injuries. The shoulder belt should go
over the shoulder and across the chest. These parts of
the body are best able to take belt restraining forces.
The safety belt locks if there's a sudden stop or crash,
or if you pull the belt very quickly out of the retractor.
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