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... To King's surprise, Cocconi proved at first patient and cooperative, and seemed privately pleased to be given a pass to enter the top secret [Hughes] facility at will. But even with his help, the inverter was a nightmare.
Cocconi, it turned out, had made notes for about 2 percent of his one-of-a-kind [Impact prototype] inverter as he created it at home. The Hughes engineers were reduced to taking pictures of his work and trying to use the pictures as diagrams. To "reverse engineer" the box, as they put it. The circuit boards were extremely difficult to map, much less reproduce, and manufacturing them seemed impossible. Most complex were the transistor switches that made the inverter work - the heart of the car, switching DC current from the batteries to AC for the motors. The transistors were both the boon and the bane of Cocconi's design.