The relay is an electrical device that controls the lighting by acting as a switch. According on the vehicle's specific needs, they come in a range of shapes, sizes, and designs.
When current is given to the relay, the circuit within cuts on and off, resulting in the relay clicking sound and the turn signal or danger lights blinking.
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).
Are you aware that, according to an online MOT history checker, one of the most prevalent reasons for a MOT test failure is the lights? The bulbs in your car's high and low beams, left/right indicators, hazards, and other lights may need to be replaced.