We naively thought we could swap a couple of sconce lights, but this is what we found
Neither of the existing lights was mounted in a box, instead there was a “clever” surface mounting method used, with the wires and marrettes tucked into little cavities. I see why this was done, especially on the exterior wall, since there is not enough space for a standard size octagon box between the brick and the drywall. We have about a one inch gap, then lathe, then the drywall.
I’ll see if I can find and install a shallow octagon box instead. It will be tricky to do so, because there are no studs to connect to, and not enough space to retrofit any into the wall. As Sofia said, “nothing is ever easy, is it.”