Another handy tool to use is a non-contact (inductive) ammeter. I picked one up on Amazon for $40 when chasing a draw and it has been consistent and pretty accurate. All you have to do is put the clamp around a wire (or wiring harness) and it will tell you instantly how much current is flowing within, so you can chase where it's headed.
Price went up a few bucks, URL was too long for software to recognize, here's the link: Amazon Inductive Ammeter Link