A normally-open contact closes with the lever up. A normally-closed contact (marked with a bar) closes with the lever down. Two paths in parallel close if either one of them closes.
The arc only strikes with the warning lamps in this exact combination. And mind the levers: the generator's brushes are worn down, so twelve switches count. You can throw more, but every extra one sparks and goes in the log. Work out the diagram before you touch anything.
The projector's arc won't strike unless the switchboard is in the right position, and the right position isn't written down: it's drawn. Six levers, five warning lamps, and a contact diagram pinned to the wall. Twelve switches count before the brushes start sparking, so this isn't something you find by trial and error.
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