Have you looked for a burnt fusible link? I'm not sure what you're working on, but since you've done all the other things I would look at, it seems like a broken or burnt wire to me. I don't know if your car even has fusible links, but if so, check them. They burn in half internally, so if you find some, just grab the wire in each hand and pull on it like you're stretching a rubber band. If it's burned in half, the wire will stretch.