Why an older EM shows no GI until a game starts
EMs built before about 1970, especially Gottliebs, often have no power switch at all. On Gottlieb the general illumination only turns on once a game is started; on Williams and Bally (as late as 1977) pressing the left flipper button usually turns the GI on. Neither is a fault.
Systems
Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part Two, Clay Harrell (pinrepair.com)