Probably either the GI connectors on the interconnect board in the bottom of the backbox or the connectors on the GI relay mounted behind the swing out light panel in the backbox. The GI power from the transformer goes to the GI input on the right top side of the interconnect board, then through fuses and then out connectors below the fuses to the cabinet and backbox. Do any connectors looked burned? If so replace. If not, try reseating the connectors and see if you can get them to turn on. They're probably tarnished and will need replacing anyways. Do the same with the connectors on the GI relays They get burned too and need replaced, but try reseating and see if the lights come back on. IIRC, there's another GI connector on the interconnect board farther left somewhere. The connectors are labeled, so look for whatever ones are marked GI.