Any Idea what Small Battery Wire is For

[kernie]

I have a small pos/neg wire coming from under the car and (neg) connecting to frame, (pos) connecting via fuse to positive battery terminal. Any idea what this wire is for. As I was cleaning near the battery terminal, I noticed this wire (pos) had burned from the header heat, the fuse is also blown, but nothing noticable is wrong.

Any ideas?

 

[Ulysses]

Goes to a bank of relays that can affect all kinds of things, even driveability and startability.