During an ILS approach at night to runway 2 at Nadi, (Fiji, the no. 2 electrical system failed. A little later, during final approach, the aural warning for non-extension of landing gear sounded. The crew decided to continue the approach. On landing, the airplane exited the runway to the right and came to a stop leaning on the fuselage. Examination of the airplane showed that the landing gear was retracted with the landing gear doors open. The landing on the fuselage resulted from an incomplete analysis by the crew of the consequences of the electrical failure and the warning that triggered during the final approach. The airplane operated on a repositioning flight from New Caledonia to Wallis Island via Nadi, Fiji, in preparation for medevac flight. Causes of the Accident: At night in adverse meteorological conditions, the crew decided to continue with the approach and to land, while the landing gear was not locked in the down position due to the failure of the secondary electric circuit. The origin of this failure was probably the increase in the number of operating cycles of the hydraulic power pack which delivers the hydraulic energy required to extend and retract the landing gear. This led to the failure of the diodes in the protective secondary circuit, which could not be checked in flight. The decision to continue the approach resulted from incorrect comprehension of the electrical failure and the aural warning that sounded during the final approach. The conviction that the landing gear was locked down, associated with the meteorological conditions and the failure of the circuit-breakers to trip, did not prompt the crew to correctly assess the risk associated with the electrical failure.