What was found
WITH THE APU ON & BLEED AIR SELECTED ON, SMELL AN ELECTRICAL BURNING. TRACKED ODOR BACK TO LT SIDE OVERHEAD HEAT DUCT. WHEN TOUCHED, METAL TRACK WHERE THE HEATER DUCT IS THAT HOUSES AN OVERHEAD LIGHT STRIP, TOO HOT TO TOUCH & HAS A BURNING ODOR. HEAT IS TRANSFERRING TO ROOF LINER. ODOR IS MORE ELECTRICAL. RT SIDE OVERHEAD HEAT DUCT IS SLIGHTLY HIGHER THAN ROOM TEMP & NO ODOR. RAN APU FOR OVER AN HR W/LIGHTS & HEAT ON, NO ODORL. PULLED BOTH C/BS, OVERHEAD FLOOD LIGHT PANEL & ALL 3 SCREENS. NO ODOR SMELL. APU RUNNING ALSO WENT BACK INTO THE TAIL E BAY, NO ODOR . RAN APU & INSP COCKPIT FOR ANY ODOR. NO ODOR NOTED. MCC OK TO PROCEED WITH RELEASING AIRCRAFT.