GMC 2007 Sierra - Manual (Page 225)

Fog Lamps
If your vehicle has fog lamps, use them for better
vision in foggy or misty conditions.
The fog lamp button is
located on the left side
of the instrument
panel.
The parking lamps and/or low-beam headlamps
must be on for the fog lamps to work.
Press the button to turn the fog lamps on or off.
An indicator light will glow in the button when
the fog lamps are on.
Remember, fog lamps alone will not give off as
much light as the headlamps. Never use the
fog lamps in the dark without turning on the
headlamps.
The fog lamps will go off whenever the high-beam
headlamps come on. When the high beams go
off, the fog lamps will come on again.
The fog lamps will be cancelled after the ignition is
turned off. If you still want to use the fog lamps
after you restart the vehicle, you will need to press
the fog lamp button again.
Some localities have laws that require the
headlamps to be on along with the fog lamps.
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