wiring smoking!

[alden]

I thought I had the wiring figured out so I decided to hook up the battery and test lights etc, but when I did that all of a sudden my wiring started smoking and crackling.

I don't have the headlight switch or the lights hooked up but didn't think that would be a problem. I didn't even get around to turning the key, it just started crackling immediately so I unhooked it before I started a fire. What could I have possibly done so wrong?