pitchshifter

I have a 97 mustang GT 4.6 dual over head cam that i have recently acquired and is having starter problems. When i turn the ignition to start it wont do a thing. But if i get underneath the car and take a jumper wire and touch the big hot wire and jump to the post where the black wire goes it will start. So its not the starter, my question is where does that black wire go to? Does it go to the fuse box or somewhere else? Is it on a relay? Any help would be appreciated.