Well if all else fails and you can afford it, I recommend a good electrical shop. It may end up being less painful to just bite the bullet and have someone else troubleshoot. I had a similar problem with my truck and it was a bad wiring harness that I had no clue about. I ended up spending over 100 bucks on miscelaneous parts, and it turned out to be a few 25 cent terminals and 60 bucks in labor to find them.  Good luck!