Check for a stuck contact on the GI relay.

If the playfield lights go out at "blackout", the relay coil circuit must be OK since the relay does pull in. So, as Inkochnito said, there must be something wrong with the GI wiring. According to the schematic, the "blackout" relay cuts power to all general illumination. Check that your yellow and white/yellow wires are connected like the schematic.
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