So a sort of tangential issue to my boarding lights problem has come up. Can someone give me an idea of how the bulkheads - specifically in the salon area - are constructed? I'm likely going to need to fish new wires through the walls and I can't wrap my head around how they're put together.

From the small-diameter hole on the exterior side of the salon bulkhead (where the boarding lights are mounted), I can see into the cavity. It looks to be several inches thick, which surprised me. I was hoping the wires were just loose in the cavity but they're not loose at all - they're very securely attached to something, meaning I can't use the old wires to pull the new wires through.

Unfortunately I think that means I'm going to have to disassemble something to complete this project.