On September 7, 2009 at approximately 2100 EDT a Delta Air Lines (DAL) 767, N840MH, operating as flight 186, was two hours enroute from John F. Kennedy International Airport (JFK) to Venice Marco Polo Airport (VCE), when the cabin lights flickered, the Passenger Address System was intermittent and then inop, the left side oxygen masks deployed and a sulphur smell was observed, but no smoke. The flight diverted to ATL and landed without incident. There were 206 passengers, 8 cabin crew and three flight crew and no injuries were reported. DAL maintenance crews examined the area above the forward lavatory on the left side and found a wire bundle which had numerous fractured and melted wires, with soot on the bundle and immediate area. There were also signs of chaffing on a piece of support structure near the cable routing. A review of the Boeing wire installation drawings revealed that the damaged wire bundle was routed incorrectly and not properly secured. DAL performed a fleet inspection and found one other airplane with this wire bundle incorrectly routed. It was not damaged and they corrected the installation. The investigation did not determine if the incorrect routing occurred during manufacturing, maintenance, or modifications. A review of the wires in the bundle confirmed that oxygen system, passenger address system, and lavatory power wires were included in the bundle.