GMC 1999 Sierra 1500 Pickup Owner's Manual page 123

Daytime Running Lights (DRL) Indicator Light (Canada Only)
K2318
If your vehicle was first sold, when new, in Canada, you will have this light on
the instrument panel. It goes on whenever the Daytime Running Lights are on.
Daytime Running Lights (Canada Only)
The Canadian Federal Government has decided that "Daytime Running
Lights" (DRL) are a useful feature, in that DRL can make your vehicle more
visible to pedestrians and other drivers during daylight hours. DRL are
required on new vehicles sold in Canada.
The high beam headlights will come on at reduced brightness in daylight
when:
The ignition is on
The headlight switch is
off, and
The parking brake is released
When you turn on your headlights, the DRL will switch off and the exterior
lights will come on. When you turn off the headlights, the exterior lights will
go out and the high beam lights will switch to the reduced brightness of DRL
again. The DRL indicator light on the instrument panel will go on whenever
the DRL are on. This light means that only the DRL are on. When you turn
on your exterior lights, this light will go out. Of course, you may still turn on
the headlights any time you need to.
To idle your vehicle with the DRL off, set the parking brake. The DRL will
stay off until you release the parking brake.
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