GI passes through the interconnect board. The interconnect board is often a source of these types of problems. pinwiki has good information:

https://pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#Repairing_the_General_Illumination_Input_Connector_.2F_Wiring

You can also search pinside for "Interconnect board".

The Police Force interconnect board will look the same as the one in WW. However, the components are different from game to game due to differences in the flash bulb strings.

Using the color coded image on pin wiki you can troubleshoot your WW board using a meter.