What happened and why?

[drewbert41]

I got my truck running for the first time since rewiring, adding a new fuel line, relocating my alternator, adding headers, and adding a starter heat shield. Rebuilt the carb and got the truck running the way I wanted.

I went to start the truck the next time and heard an arc. Looked under the hood and found this. Either burnt or fried battery cable.

I am guessing it arced to the heat shield? Weird how it ran fine and then this happened. I don't think my headers would have melted it would they? My alternator wire and plug wires aren't melted.