What does the red voltage light indicate?

The red voltage light serves as an important indicator of the aircraft's electrical system condition. When this light illuminates, it signifies that the electrical voltage is either outside the acceptable range, indicating an overcharging or undercharging situation. This can lead to inadequate power supply for the aircraft's systems or potential damage to components if the alternator is supplying too much voltage.

The other options relate to specific failures or malfunctions that could also impact the electrical system. A failed alternator would typically result in a total loss of electrical power rather than just a voltage anomaly, which is more accurately reflected in the red light for voltage issues. Similarly, an electrical system failure encompasses a broader range of potential problems, not just the state of voltage, while a malfunctioning battery might cause operational issues but may not specifically illuminate the voltage light unless tied to the charging status affecting system voltage.