What I would try... With that plug disconnected from trans, use a jumper across the outer 2 wires to make the reverse lamp circuit. If the fuse blows again the short is in reverse lamp circuit, wiring or fixtures. If this is, or once was, a manual trans car with a reverse indicator in the dash, the short could be there too.
I will give that a try as well. I have to think its a problem with the switch because I noticed it would start in any gear. Its an automatic. Thanks for your help, Ill post the final outcome on Monday when I get a little more time to work on it.
