Lexus GX470 2004 Owner's Manual page 161

OCCUPANT RESTRAINT SYSTEMS
Two buckles and tabs for third center seat belt.
The 2 buckles for the third center seat belt are distinguished
with colors of the buckle release button. Also the 2 tabs have
different shape for its end so that the belt is not buckled in the
wrong place.
1 Buckle with light gray buckle-release button:
Properly matches with concave end tab
2 Buckle with red buckle-release button:
Properly matches with round end tab
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To release the concave end tab, insert the key into the hole on
buckle with light gray buckle-release button and allow the belt
to retract.