THE PLT RPRTD THAT THIS WAS A POSITIONING FLT FOR A 100 HR INSPN & THAT THE ACFT WAS HAVING ELECTRICAL PROBLEMS THRU-OUT THE FLT. ACCORDING TO HIM, HE EXTENDED THE FLAPS & PUT THE GEAR HANDLE IN THE DOWN POSITION AS HE MADE A VOR APCH AT NIGHT; HOWEVER, THE ACFT TOUCHED DOWN WITH THE LANDING GEAR RETRACTED. DURING THE WHEELS UP LANDING, A FIRE OCCURRED IN THE COCKPIT AREA, EXTENSIVELY DAMAGING THE INSTRUMENT PANEL, BUT THE ORIGIN OF THE FIRE WAS NOT VERIFIED. THE LANDING GEAR UPLOCKS WERE FOUND UNLATCHED, BUT THE WHEELS WERE FOUND IN THEIR RESPECTIVE WHEEL WELLS. AFTER THE ACFT WAS HOISTED OFF THE GROUND, ALL THREE WHEELS EXTENDED WITH NO DIFFICULTY WHEN THE EMERGENCY EXTENSION SYS WAS OPERATED. NEITHER THE ELECTRICAL GEAR MOTOR NOR THE INSIDE OF THE GEAR MOTOR COMPARTMENT WERE BURNED IN THE FIRE, BUT THE MOTOR HAD EVIDENCE OF THERMAL OVERLOAD DAMAGE AROUND THE WINDING. NO INFO WAS RECORDED ON THE TOWER TAPES TO INDICATE A GEAR PROBLEM BEFORE THE ACFT LANDED.