Melted ground wire?

[Dagger Thrasher]

Hmmm...that's bizarre, to say the least. You say the wire was melted its entire length? Was it just the insulation? If it's like I think you're saying, then perhaps you somehow accidentally shorted out the BEC; maybe a servo died or something. The smoke could well have been the linear regulator going south.

Do you have any photos? It might be easier to see what you mean, but it sounds like somehow the BEC has shorted to me. It'll probably mean a trip to CC HQ though, I'm afraid.