GMC 2007 Sierra - Manual (Page 213)

Other Warning Devices
If you carry reflective triangles, you can set them
up at the side of the road about 300 feet (100 m)
behind your vehicle.
Horn
To sound the horn, press the center pad on the
steering wheel.
Tilt Wheel
The tilt wheel will allow you to adjust the steering
wheel before you drive. Raise it to the highest
level to give your legs more room when you exit
and enter your vehicle.
The tilt steering wheel lever is located on the
lower left side of the column.
To tilt the wheel, hold the steering wheel and pull
the lever. Then move the steering wheel to a
comfortable position and release the lever to lock
the wheel in place.
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