Quoted from schudel5:There are connectors on the interconnect board in the backbox that carry the GI power from the transformer to the game. The interconnect board is the one on the very bottom in the backbox. The GI wiring and fuses are all on the right side of that board. It's labeled showing the input from the transformer, fuses and outputs to the backbox and playfield. Those .156" headers and connectors for the GI get burned and will need replacing.
Also, under the playfield and behind the backbox light panel is a GI relay. These relays are used to flash the GI and the .156" connectors on those get burned too causing the same lighting issues.
Most of the problems with GI can be attributed to bad IDC connectors. Use a meter to determine if the GI voltage is making it off a connector. For example, you'll have an IDC connector that you can check for voltage on the top at the little pinch pins, but you can't really tell if it is making it through the insulation and to the stranded conductor inside. From there you need to measure voltage at that wires end destination.
The AC GI circuits come off the interconnect in pairs of a solid color and a striped wire of that solid color for each branch on this series of games. For example, measuring across solid violet wire to the white/violet striped wire should reveal the GI supply voltage.