Cadillac 2003 Seville Owner's Manual page 27

Lap-§boulder Belt
2. Push the latch plate into the buckle until it clicks.
All rear seating positions have lap-shoulder belts. Here's
how to wear one properly.
1. Pick up the latch plate and pull the belt across you.
Don't let it get twisted.
The shoulder belt may lock if you pull the belt
across you very quickly. If this happens, let the belt
go back slightly to unlock it. Then pull the belt
across you more slowly.
If the belt stops before it reaches the buckle, tilt
the latch plate and keep pulling until you can
buckle it.
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 1-23.
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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