GMC Yukon 2015 Owner's Manual page 126

2.2. Route, attach, and tighten
the top tether according to
your child restraint
instructions and the
following instructions:
If the position you are using
does not have a head
restraint and you are using
a single tether, route the
tether over the seatback.
Seats and Restraints
If the position you are using
does not have a head
restraint and you are using
a dual tether, route the
tether over the seatback.
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