Houdini never revealed the secret of his mind reading feat. But after his death, his nephew, Louis Kraus, did. In doing so, he also revealed one of the secrets of 278. Kraus's lengthy explanation was reprinted in Houdini The Key by Pat Culliton. Below is a key excerpt:
"The whole house at 278 West 113th Street was wired. The room in which the committee sat was so completely wired that the least whisper was picked up and carried electrically to an operator concealed in the basement. The operator held a transmitter in his hand and repeated all he heard. His repetitions were carried by other hidden wires to the top floor, terminating in loops under the carpet. In this way, the spoken thoughts of the committee in New York, were actually carried to the magician, invisibly through wire and air, but the method was electrical not telepathic..."
So is this mysterious wire part of Houdini's secret mind reading system? I think it almost certainly is. And while a few pieces of wire needed to be removed, most of it will remain as a historic part of Houdini's 278.
UPDATE: The following is from a lengthy profile of Amedeo Vacca in the December 1947 The Linking Ring. In it Vacca says he was the man who wired the walls of 278 for Houdini's mind reading trick. It then says: