THE ACFT WAS ON AN INSTRUMENT FLT PLAN. THE PLT HAD RECEIVED A PRE TAKEOFF WEATHER BRIEFING. HE WAS BRIEFED ON THE AREA OF WEATHER THAT WAS AT THE ACFT'S TWELVE O'CLOCK POSITION FOUR MILES IN FRONT. THE AREA WAS THIRTY MILES SOUTHWEST AND TWENTY MILES WIDE. THE PILOT STATED HE HAD A SLIGHTLY HOT ENGINE RIDES OR ONE WAS A LITTLE ROUGH. THE AIRCRAFT WAS CLEARED TO SHREVEPORT, GIVEN VECTORS ANS DESCENDED. ALL RADIO AND RADAR CONTACT WAS LOST AT ABOUT 4000 FEET. NO MALFUNCTIONS WERE NOTED ON EITHER ENGINE. NO KNOWN MALFUNCTION FOUND WITH ACFT. TAIL LIGHT BULB FILAMENT SHOWED NO DIRECT CURRENT BEING APPLIED AT IMPACT. POSSIBILITY OF INFLIGHT LOSS OF DC POWER CAUSING PILOT TO LOSE CONTROL OF AIRCRAFT DURING DARK NIGHT AND TURBULENT INSTRUMENT FLIGHT. AIRCRAFT ALLOWED TO IMPACT SURFACE IN NEAR PAST VERTICAL NOSE DOWN ATTITUDE. POSSIBLE INADVERTENT ACTIVATION OF CRASH BAR LOSS OF ALL ELECTRICAL. POSSIBLE PASSENGER MOTION SICKNESS