A B767-200; DURING A CABIN LIGHTING CHECK A CEILING FLO LIGHT ASSEMBLY WAS FOUND WITH 6 INCHES OF WIRE INTERMITTENTLY SHORTED TO STRUCTURE WITH BURNED INSULATION.

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WHILE RELAMPING CEILING LIGHT ASSY WXZ; HEARD SIZZLING SOUND. FOUND LIGHT ASSY WIRING APPROX 6 INCHES. AFT OF AFT LIGHT SOCKET ARCING AND SPARKING. AFTER TURNING OFF CEILING LIGHTS; FOUND SMALL FLAME BURNING ON WIRING INSULATION. SUSPECT WIRES HAD RUBBED ON ACFT METAL STRUCTURE; RUBBING THROUGH WIRE INSULATION UNTIL PWR WIRES AND CHASSIS GND WERE TOUCHING. FOREMAN TOOK PICTURES AND WIRING WAS GIVEN TO FOREMAN TO PASS ON TO CORRECT PEOPLE FOR EVAL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED WHEN WALKING IN THE AISLE CHECKING THE OVERHEAD CEILING LIGHTS A SIZZLING NOISE WAS HEARD AND ON OPENING THE LIGHT ASSEMBLY THE AFT SOCKET WIRING WAS SEEN TO BE ARCING. THE RPTR SAID WHEN SWITCHING OFF THE CEILING LIGHT THE INSULATION WAS BURNING WITH A 1.5 TO 2 INCH FLAME. THE RPTR STATED THE FLO LIGHT BALLAST IS FUSED WITH A REPLACEABLE FUSE; BUT WAS NOT FOUND OPENED. THE RPTR SAID THE WIRING WAS BURNED TO ABOUT 6 INCHES FROM THE SOCKET AND WAS NOT SECURED; ALLOWING IT TO CHAFF ON ACFT STRUCTURE INTERMITTENTLY SHORTING THE WIRING.