If an aircraft ammeter indicates a negative value, what does this imply?

When an aircraft ammeter indicates a negative value, it typically means that the generator or alternator output is inadequate to meet the electrical demands of the aircraft's systems. In this scenario, the electrical load being drawn from the battery exceeds what the generator can supply, leading to a discharge from the battery. As a result, the ammeter reflects this condition as a negative reading.

A functioning generator or alternator should maintain a neutral or positive output under normal operating conditions. When the output is insufficient, the battery compensates by supplying the necessary current, which is what generates that negative reading on the ammeter. Therefore, recognizing a negative ammeter reading is critical for addressing potential issues with the aircraft's electrical system and ensuring that all components have the power they need to function correctly.