What should I do if I need to use the car seat without the built-in harness?

You must use a vehicle lap/shoulder belt to secure your child and the booster seat—LATCH will not secure your child in the booster seat. Place the child in the car seat with their back flat against the back. Position the lap/shoulder belt as shown, fasten the buckle, and pull up on the shoulder belt to tighten. If the belt crosses the child's neck, head, or face, use the shoulder belt positioner to redirect the belt across the chest. (Pages 28-30)