GMC 2003 GMT560 T-Series, Owner'S Manual

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When the DRL are on, only your headlamps will be on.
The taillamps, sidemarker and other lamps won’t be
on. Your instrument panel won’t be lit up either.
When it begins to get dark,
your DRL indicator light is
a reminder to turn the
headlamps on. The other
lamps that come on
with your headlamps, will
also come on.
When you turn the headlamps off, the regular lamps will
go off, and your low-beam headlamps will change to
the reduced brightness of DRL.
To idle your vehicle with the DRL off, set the parking
brake. The DRL will stay off until you release the parking
brake.
As with any vehicle, you should turn on the regular
headlamp system when you need it.
Marker Lamp Defeat Switch
If your vehicle has this feature, you can manually blink
the marker and clearance lamps.
The marker lamp defeat
switch is located in the
instrument panel
switchbank.
Press and hold the bottom of the switch to turn off the
marker and clearance lamps. When you release
the switch, the marker and clearance lamps will come
back on.
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