Pontiac 1998 Firebird Owner's Manual page 22

If the belt stops before it reaches the buckle, tilt
the latch plate and keep pulling until you can buckle
the belt.
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.
5. To make the lap part tight, pull down on the buckle
end of the belt as you pull up on the shoulder belt.
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