Which maintenance fault does NOT illuminate a light with a unit number?

In the context of maintenance faults, the Sanders fault is the one that does not illuminate a light with a unit number. This is because the Sanders system, which relates to the sanding function often used on trains to improve traction or prevent wheel slip, typically operates without a direct diagnostic or monitoring light that corresponds to a specific unit number.

In contrast, faults like the EP Brakes not releasing, compressor faults, and HVAC failures generally trigger specific alerts or indications that help operators identify the fault's location and operational impact. These systems are more integrated into the unit’s fault detection and reporting mechanisms, allowing for more immediate identification and troubleshooting.

Therefore, the absence of a light with a unit number in the case of a Sanders fault makes it the correct choice, as it highlights a flaw in the visual alert system pertaining to this specific maintenance issue. Understanding the operational nuances of these systems can significantly improve diagnostic skills and fault resolution in maintenance scenarios.