When I first started this layout, I wasn't sure if Hill City had electricity in 1920. I've since learned that there was indeed electricity available, which led to me put lights in the depot. The product warehouse was finished long before this discovery, so it didn't get lighting installed. Until now.
Complicating the installation of lighting is the removable roof and/or rafters on the warehouse. I built it so that it can be displayed with no roof at all, or with just the rafters exposed. I didn't want lighting to interfere with this, or to force me to permanently attach the rafters. Using small-diameter brass rod, I found a way to install the lighting and keep the roof and rafters removable.
I made power feeders using the brass rod, running the rod along the rafters, just like electrical conduit is done in real life. Once this is painted with some dark brown paint, it should essentially disappear, blending in to the rafters themselves.
If you look closely at that last photo, you'll notice two pieces of brass rod running vertically down the back wall. Those are my temporary leads that go down through the floor and to the main layout power. To facilitate the removable rafter concept, I'm going to replace these with smaller diameter rod. Where you see these now, I'll be installed two pieces of brass tubing, large enough to accommodate the smaller diameter rod. The tubing will be attached to the layout power, the rod will be attached to the power grid hidden in the rafters. When the rafters are on the structure, the rods will go inside the brass tubing, providing the electrical connectivity to power the lights. When removing the rafters, the rods will simply slide out of the brass tubing.