GMC 2004 Sierra 1500 Pickup Owner's Manual page 62

If your child restraint is equipped with the LATCH
system, see Lower Anchorages and Top Tethers for
Children (LATCH System) on page 1-48 . See Top Strap
on page 1-43 if the child restraint has one.
If your child restraint does not have the LATCH system,
you'll be using the lap-shoulder belt to secure the child
restraint in this position. 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.
1-56
3. Buckle the belt. Make sure the release button is
positioned so you would be able to unbuckle the
safety belt quickly if you ever had to.