Pontiac 2003 Bonneville Owner's Manual page 45

Anchor the top strap to one of the following anchor
points. Be sure to use an anchor point located on the
same side of the vehicle as the seating position
where the child restraint will be placed.
Once you have the top strap anchored, you'll be ready
to secure the child restraint itself. Tighten the top
strap when and as the child restraint manufacturer's
instructions say.
Top Strap Anchor Location
Your vehicle has top strap anchors already installed for
the rear seating positions. You'll find them behind
the rear seat on the filler panel.
In order to get to a bracket, you'll have to open the
trim cover.
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