Yet another ground related issue. The grounds for the display light driver board go to the regulator board connector and deteriorate over time. The simple solution is to try my ground upgrades before doing anything else:
https://www.flippers.com/gottlieb_ground_cures.html
You want the System 80 section.
This fixes most problems in Gottlieb pins, once the ground upgrades are done then you can look for the causes of other troubles.