I need to do the opposite of what is talked about in this post: Can I convert ceiling mounted octagon box to electrical receptacle?
Specifically, there is a rectangular electrical box in my ceiling that I want to hang a light from. There is currently no outlet, switch, or other equipment hooked up to it - it has a solid cover screwed over the top of it. I am fairly certain that it is simply acting as a junction box for two independent sets of lights that are in the ceiling.
Any advice for how to go about this? Do I just cut out the old box and insert an old-work octagon into it? Conversely, is there a simple way to hang a ceiling light from a rectangular box?