radio fuse blows when engine starts

[natedogg]

My 85 has the original radio and it plays fine until I start the truck and the fuse blows immediately. I took the radio out and traced the black ground wire on the harness and cant find anything obvious. Any Ideas? My second question is, what is this wire in the second pic? It was hanging under the dash. Its black with a blue or green stripe. Thanks for any help. I have already fixed several little problems with my truck with help from this great site