Flasher units control how your vehicle's flashers work. Having a properly working flasher unit is crucial for your safety on the road. Without it, you wouldn't be able to properly signal your turns or lane changes to other drivers on the road, nor would you be able to operate the vehicle's hazard lights. While a failed flasher lamp is one reason a flasher may not function, if a bulb is still functional but the flasher isn't operating, it's likely that the flasher unit needs to be replaced. Flasher units can fail for a variety of reasons, including having the wrong flasher bulbs installed or exceeding the wattage recommended for the unit.