In a nine-month investigation by NewsChannel 5 (Nashville, Tenn.), Phil Williams shows that the wiring used on many planes "should not be used for airborne application."
From reading the article I discovered that Williams found test videos revealing issues with these types of wire came from the Federal Aviation Administration's own files. He also used a scientific report from the FAA's own experts calling the wires unfit for use on aircraft. There is also a listing of which aircraft have "Kapton" and PVC/Nylon wiring on the station's website.
Williams would have had to be very familiar with the FAA website and navigating the files. He would have needed to know how to access the databases as well as understand what they said. He also uses several sources to discuss the issues so he is very well connected or knew how to find these people in the databases.