The pilot’s misdiagnosis of an erroneous engine instrument indication and his subsequent decision to enter an autorotation, which resulted in a hard landing due to degraded visual cues and low ambient light conditions. Contributing to the accident were the erroneous engine indications likely caused by an undetermined electrical supply disruption; time pressure, pilot fatigue, and plan continuation bias as daylight diminished and the crew aimed to complete the flight; and cognitive overload from multiple airframe and engine caution indications.