1999 GMC Sonoma Owner's Manual - Page 206

yellowblue Hazard Warning Flashers Press the button on top of the steering column all the way down to make your front and rear turn signal lamps flash on and off. Your hazard warning flashers work no matter what position your key is in, and even if the key isn't in. To turn off the flashers, press the button until the first click and release. Your hazard warning flashers let you warn others. They also let police know you have a problem. Your front and rear turn signal lamps will flash on and off. When the hazard warning flashers are on, your turn signals won't work. The flashers will stop if you step on the brake. Other Warning Devices If you carry reflective triangles, you can set one up at the side of the road about 300 feet (100 m) behind your vehicle. 5-2