GMC 2010 Yukon/Yukon XL Owner's Manual page 232

It controls the following systems:
Headlamps
Taillamps
Parking Lamps
License Plate Lamps
Instrument Panel Lights
The exterior lamps control has four positions:
Turns off the automatic headlamps and
daytime running lamps (DRL). Turning the headlamp
control to the off position again turns the automatic
headlamps or DRL back on.
For vehicles first sold in Canada, the off position only
works for vehicles that are shifted into the P (Park)
position.
4-10
The exterior lamps
control is located on the
instrument panel to the
left of the steering wheel.
Automatically turns on the
headlamps at normal brightness, together with the
following:
Parking Lamps
Instrument Panel Lights
Taillamps
License Plate Lamps
Turns on the parking lamps
together with the following:
Instrument Panel Lights
Taillamps
License Plate Lamps
Turns on the headlamps together with
the following lamps listed below.
Parking Lamps
Instrument Panel Lights
Taillamps
License Plate Lamps