Glad you clarified. I see people blaming opto isolators all the time. It’s clear there’s something in between since it’s current rated to sink 500ma. P1 at Mouser comes back as a P-Chan mosfet, as would be expected 
Too bad you didn’t post a photo of the locations of these.
Might want to look at this thread about Control Tower Stack Lights
Thanks for the clarification… 