1994 GMC Sonoma Owner's Manual - Page 94

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. Headlights-On Reminder A reminder tone will sound when your headlights or parking lights are turned on and your ignition is in OFF, LOCK or ACC. To turn the tone off, turn the dimmer switch all the way down. Dome Light Mirrors Inside Mirror If your vehicle has optional map lights, they will automatically come on for approximately 15 seconds when either front door is opened, or until the ignition is turned to RUN or ACC.