GMC 2007 Sierra - Manual (Page 70)

If the position you are
using has an adjustable
head restraint and
you are using a dual
tether, route the
tether around the head
restraint.
If the position you are
using has an adjustable
head restraint and
you are using a single
tether, raise the
head restraint and route
the tether under the
head restraint and
in between the head
restraint posts.
1.4. Remove the trim cover to expose the
top tether anchor.
1.5. Attach the top tether attachment to the
top tether anchor.
{ CAUTION:
If the seatback is not locked, it could
move forward in a sudden stop or crash.
That could cause injury to the person
sitting there. Always push and pull on the
seatback to be sure it is locked.
1.6. Lift the seatback up and push it
rearward. Then lower the seat cushion
until the seatback and the seat cushion
lock into position.
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