Final answer:
A bad relay can cause intermittent functioning of vehicle accessories, an audible clicking sound, and difficulty starting the vehicle. Overheating might occur if the relay affecting the cooling system fails.
Step-by-step explanation:
When a relay becomes faulty, it can show multiple signs and symptoms that indicate a problem. The most common signs include the vehicle's accessories experiencing intermittent functioning such as the headlights or interior lights flickering or not working at all. Another symptom is a clicking sound coming from under the dashboard, indicating the relay may be receiving power but is not functioning properly. It indicates the compromised ability of the relay to manage electrical circuits.
Additionally, if a vital component like the fuel pump relay fails, the car may experience difficulty starting or not start at all. In cases where the relay controls the engine's cooling fans, a bad relay may lead to the engine overheating. All these symptoms suggest that the relay's ability to open and close circuits is compromised, usually due to internal wear or damage, and can severely impact the performance of the vehicle.