GMC 1999 Sierra 1500 Pickup Owner's Manual page 269

Raising your vehicle with the jack improperly positioned will damage the
vehicle or may allow the vehicle to fall off the jack. Be sure to fit the jack
lift head into the proper location before raising your vehicle.
Front Rear
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PO288
Raise the vehicle by rotating the ratchet clockwise. Make sure the UP
marking faces you. Use the jack handle extensions if the flat tire is on the
rear of the vehicle. Raise the vehicle far enough off the ground so there is
enough room for the spare tire to fit.
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