Which of the following indicates a hydraulic brake issue?

A soft brake pedal can indicate a hydraulic brake issue because it suggests that there may be a problem with the brake fluid pressure within the hydraulic system. When the brake pedal feels soft, it often means that there is air in the brake lines or a leak in the brake system, which can reduce the effectiveness of braking due to the inability of the hydraulic system to properly transmit force.

In contrast, a hard brake pedal may indicate an issue with the power assist system rather than the hydraulic system, while malfunctioning brake lights signal an electrical issue rather than directly relating to brake performance. A squeaking sound could be associated with worn brake pads or other mechanical issues but does not specifically point to vulnerabilities in hydraulic braking capability.