What was found
SMOKE WAS OBSERVED IN THE CABIN AFTER START OF TAXI TO ACTIVE RUNWAY, THE CREW SHUT DOWN ENGINES, SHUT OFF ALL POWER AND DISCONNECTED BATTERY. FOUND SOURCE OF SMOKE TO BE FROM A NO SMOKING/SEATBELT SIGN LOCATED IN THE LT SIDE OF CABIN AT FRAME 20. THE AIRCRAFT WAS SECURED AND FERRYED TO A MAINTENANCE BASE. UPON FURTHRE INVESTIAGTION, FUND NO CONCLUSIVE EVIDENCE BUT SUSPECT PROBLEM ORIGINATED AT THE INTERFACE OF THE WIRING TO THE NO SMOKING/SEATBELT SIGN.