Since I have owned this game I have always had this issue:
Lamp column 3 and 4 lights all light together even in single lamp test.
I have traced the wires and could not find any case of bridging the two column wires together. And I would think that if that did happen, it would not affect both columns entirely. Is there anything on the boards in the backbox that could be causing the two columns to light together or is the issue only under the playfield?