The spark plugs of a vehicle are essential to the motor running. They conduct the electricity of the ignition system to allow the spark that ignites the fuel system to start and run your vehicle. The number of spark plugs on a motor depends completely on the motor and how many cylinders it has. A four cylinder motor would have 4 spark plugs and so on. If one spark plug is not firing correctly, you will get a miss fire and the motor will not run properly.