The lower GI on my Whirlwind has not worked since I bought the machine several weeks ago. I have solved several other issues and finally got around to try to figure this one out. If you look VERY closely you can see the LEDs in the lower GI are VERY dimly lit so there is some current getting there. I have replaced the connector at the interconnect board (was a little brown) and reflowed/reheated the header pin solder on the relay under the playfield that the lower GI wiring goes through. The manual says the lower GI playfield is through a relay at solenoid 16.
Any ideas where to look next?