Why do my daytime running lights (head lamps) pulsate when motor is running. 2002 mazda tribute

Are the pulsing during driving or just at stops and idle? The pulse 99% of the time indicates a loose generator belt or bad alternator. YOu can have the alternator checked at a local parts store such as AUtozone, Advance, Napa, or Oreilly's free of charge. Depending on the age of your belt it may be time to change it as well. P.S. you notice your headlights because thats where your eyes are focused.. but turn your instrument light control knob all the way to brightest and willing to bet they are pulsing slightly too..