Having a taillight out, frankly, even having the light on your license plate out is a legitimate reason to stop the car. Police do not need much to stop the car. It can be something as simple as something hanging from your rearview mirror. All it takes is a simple traffic violation, and the police have the right to come into contact with you. How that contact progresses requires a different standard, but all that is required to stop you is reasonable and articulable suspicion of a criminal or a traffic offense.