What is a common sign of a failing alternator?

A dim or flickering headlights is a common sign of a failing alternator because the alternator is responsible for charging the vehicle's battery and supplying power to the electrical systems while the engine is running. If the alternator begins to fail, it may not be able to maintain a steady flow of electricity to the headlights and other electrical components. This can result in a noticeable dimming or flickering of the lights, especially at lower engine speeds when the alternator is not producing as much power. In addition, you may experience other electrical issues in the vehicle as various components fail to receive adequate power.

The other options do not directly relate to alternator failure. Increased fuel efficiency would generally indicate that the vehicle is performing well and is not a symptom of alternator problems. Higher engine temperature is more indicative of cooling system issues or engine malfunctions rather than an alternator issue. Unusual tire wear typically stems from alignment or suspension problems, not from alternator performance. Thus, dim or flickering headlights is a clear and common symptom of an alternator on the verge of failure.