How can I find an interior wall from the crawl space?
One way to locate the wall base location in the crawl space is to go ahead and make the cutout for your component cable wall box and cover plates. Such wall plate may look similar to this:



Then using a long flexy drill bit of this type:



You can then drill down through the wall base into the crawl space. Leave the drill bit in the hole so you can see it in the crawl space.