Ugh. Broke the bottom left sniper the other night so I changed it with the one in the left orbit since that one's missing the spring & was unplugged.
Unplugged the front one, removed the mechs, changed the snipers, installed the mechs & plugged the front one in. Now, in attract mode when the chaser lights go on, the GI goes out. It also goes out when it spells Raven after pushing start & while counting bonuses.
I don't see how it could be a wiring problem, but I guess I'll be spending the evening jiggling wires to try to see which one's the culprit. Should be fun!