Buick 1998 Century Owner's Manual page 54

2. If the lap-shoulder harness is buckled, unlatch it by
pushing the button on the buckle.
3. Place the child on the child restraint cushion.
4. Select only one side of the harness. Pull the lap part
of the harness out, and place the harness over the
child's shoulder.
If both sides of the harness are pulled out, the lap
parts will lock. If the lap parts lock, let both sides of
the harness go back all the way so each side will
move freely again. Then repeat this step, pulling
only one side of the harness out.
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