2013 Toyota Tundra Regular Cab Owners Manual - Page 117
2013 Toyota Tundra Regular Cab Manual
Page 117 highlights
1-7. Safety information While pushing the child seat down into the rear seat, allow the shoulder belt to retract until the child seat is securely in place. After the shoulder belt has retracted to a point where there is no slack in the belt, pull the belt to check that it cannot be extended.