Not sure about the lane change lights, but if you can see even a little glow inside the 4th player glass than it is likely to be the control chip. If there is no glow at all, it is probably out gassed. Lots of alternatives there if that is the case. As for testing it, fully swap between another player and see that the known working display does work in the fourth player position, not just that the fourth display does not work in another position. That will confirm it is just the display and not anything else.

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