Check all the relevant wires and connections that keep the ignition working: switch, battery, ECU, coil or equivalent, including earths. Visual inspection, wiggle, disconnect, clean, reconnect. And the same for the alternator. Measure the battery voltage at rest, minimum during cranking and at 3,000 rpm.... When the car lost power what happened to the lights... unaffected, total failure, dimmed... ? ... Does the ignition warning light behave normally: on with the key, off as soon as the engine's running? ... Any recent work on the car? ... Do you have the appropriate wiring diagram? Jonathan