GMC 2003 Safari Owner's Manual page 62

You'll be using the lap-shoulder belt. See Top Strap on
page 7-48 if the child restraint has one. Be sure to
follow the instructions that came with the child restraint.
Secure the child in the child restraint when and as
the instructions say.
1. Put the restraint on the seat.
2. Pick up the latch plate and run the lap and shoulder
portions of the vehicle's safety belt through or
around the restraint. The child restraint instructions
will show you how.
3. Tilt the latch plate to adjust the belt if needed.
1-55