While flashers are a basic component in both design and function, they play a significant part in a vehicle’s overall driveability and can jeopardise safety if they fail. If you check MOT history of your vehicle and realise a previous MOT failed due to the lights not working, there could be two reasons for this. Either the bulb(s) had blown, or it was a faulty relay. To confirm this go through any previous repair invoices (if available).