Many years ago I saw a programme on an air incident investigation. They were examining the cockpit wiring, with a video camera set up. At one point, they had a question about whether the wiring had been installed correctly. They went back and checked the video - IIRC the wiring had been incorrectly installed, which was one of the root causes of the crash.<p>Ever since then, any time I need to work with existing wiring, I always photograph it first.