Buick 2004 Rendezvous Owner's Manual page 66

Your vehicle has top strap anchors already installed for
the rear seating positions. An anchor bar for a top
strap is located at the rear of the seat cushion for each
second row outboard seating position. The anchor
bar for the center position bench seat is located on the
floor behind the second row seats. If the vehicle has
the extended rear convenience center, you need
to remove a plastic plug and look under the convenience
center to find the anchor bar for the center position
bench seat.
Do not use a child restraint with a top strap in the right
front passenger's position, because there is no place
to anchor the top strap.
1-60
Second Row Center Position Bench Seat with Third
Row Seat
If the vehicle has a third row seat and the seatback is
upright, there is an anchor strap located between the third
row seatback and cushion to anchor the child restraint for
the second row center position bench seat.