A bad ignition switch can cause a car not to start or to die suddenly while being driven. It can also cause electrical components, such as the lights and radio, to stop working.
The ignition switch carries power from the battery to all the electrical components and the starter. If the ignition switch goes bad, these parts do not receive power and cannot work. If the electrical contacts within the ignition switch are worn out, the car may start and then die. This is because the heat and vibration from the moving car causes the engine to momentarily lose power.