1998 GMC Sonoma Owner's Manual - Page 104

Automatic Headlamp System When it is dark enough outside, your automatic headlamp system will turn on your headlamps at the normal brightness along with other lamps such as the taillamps, sidemarker, parking lamps and the instrument panel lights. The radio lights will also be dim. Your vehicle is equipped with a light sensor on the top of the instrument panel under the radio speaker grill so be sure it is not covered, which will cause the system to be on whenever the ignition is on. The system may also turn on your headlamps when driving through a parking garage, heavy overcast weather, a tunnel or fuelingyour vehicle in a low-light area. This is normal. There is a delay in the transition between the daytime and nighttime operation of the Daytime Running Lamps (DRL) and the automatic headlamp systems so that driving under bridges or bright overhead street lights does not affect the system. The DRL and automatic headlamp system will only be affected when the light sensor sees a change in lighting lasting longer than the delay. To idle your vehicle with the automatic headlamp system off, set the parking brake while the ignition is off. Then start your vehicle. The automatic headlamp system 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, Lamps On Reminder A reminder chime will sound when your headlamps or parking lamps are manually turned on and your ignition is in OFF, LOCK or ACCESSORY. To turn the chime off, turn the knob all the way to the left or turn the instrument panel dimmer down to the fully dimmed position. In the automatic mode, the headlamps turn off once the ignition key is in OFF. Daytime Running Lamps Daytime Running Lamps (DRL) can make it easier for others to see front of your vehicle during the the day. DRL can be helpful in many different driving conditions, but they can be especially helpful in the short periods after dawn and before sunset. 2-40