Mazda 2002 B2300 Owner's Manual page 112

Seating and Safety Restraints
Regular Cab and 4–door Cab Plus
2–door Cab Plus
To lower the shoulder belt height, push the button and slide the height
adjuster down. To raise the height of the shoulder belt, slide the height
adjuster up. Pull down on the height adjuster to make sure it is locked in
place.
WARNING: Position the safety belt height adjusters so that the
belt rests across the middle of your shoulder. Failure to adjust
the safety belt properly could reduce the effectiveness of the
seat belt and increase the risk of injury in a collision.
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