Global Machinery Company Sierra 1999 - Manual (Page 286)

yellow blue
5-26
Front Position All Other Models Rear Position
3. Make sure the jack head is positioned so that the rear
axle is resting securely between the grooves that are
on the jack head. Turn the wheel wrench clockwise
to raise the vehicle. Raise the vehicle far enough off
the ground so there is enough room for the spare tire
to fit.