Could be a number of reasons. How many miles are on the car? What kind of gas do you use? Have you used any engine cleaning agents such as seafoam? Any electrical issues that you have noticed? Dimming headlights, interior lights etc? Could be a grounding issue. Ever changed the fuel filter? I would start with the easy stuff and get your engine cleaned out. Use seafoam or some fuel system treatment. See if that helps. Then look at the electrical stuff.