Cadillac 2007 DTS Owner's Manual page 35

The latch plates for the safety belts in each rear
seating position vary in size. If the center rear
or the left rear latch plate is inserted into the
incorrect buckle, the plate will not latch properly.
Be sure you are using the correct buckle and
that the latch plate clicks when inserted into the
buckle.
When the shoulder belt is pulled out all the way,
it will lock. If it does, let it go back and start
again.
Pull up on the latch plate to make sure it is
secure.
If the belt is not long enough, see Safety Belt
Extender on page 39.
3. To make the lap part tight, pull up on the
shoulder part.
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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