Complex sentence: Insulation on the plane's intricate wiring soon became brittle and useless; during the A- 12's lifetime, no better insulation was found, and the wiring and related connectors had to be given special attention and handling at great cost in labor and time.
Split into simpler sentences: Insulation on the plane's intricate wiring soon became brittle and useless. During the lifetime of the A- 12 no better insulation was found and the wiring and related connectors had to be given special attention and handling at great cost in labor and time.