We narrowed it down to the recessed fixtures ballasts, the relay's timing was also messed up so it stayed on for hours. Naturally, people unscrewed the lightbulbs over the years. We also tested the speakers and determined some of their voice coils had been blown out. The wiring, albeit hard to follow, still works.
We are going to replace all the speakers soon, and until the pager fails to alert, it will live on.