GMC 1996 Sonoma Owner's Manual page 34

When you sit in a center seating position, you have
a
lap
safety belt, which has no retractor. To make the belt
longer,
tilt
the latch plate and pull
it
along the belt.
To make the belt shorter. pull its free end as shown until
the belt
is
snug.
Buckle, position and release
it
the way as the lap part of
a lap-shoulder belt. If the belt isn't long enough, see
"Safety Belt Extender" at the end of this section.
Make sure the release button on the buckle is positioned
so you would be able to unbuckle the safety belt quickly
if
you ever had to.
1-26