GMC TopKick 2007 Owner's Manual page 39

2. Push the latch plate into the buckle until it
clicks. Pull up on the latch plate to make
sure it is secure.
When the shoulder belt is pulled out all the
way, it will lock. If it does, let it go back all the
way and start again. If the belt is not long
enough, see Safety Belt Extender on page 41.
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.
3. To make the lap part tight, pull up on the
shoulder part.
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