88 GT cranking issue

[rivergem14]

I have 5.0L 88 Mustang gt. Recently i beagan having a cranking issue. The starter will continue to crank even with the key out. Pulling the 12v wire at the solonoid will not stop it. Solonoid is new. Starter is new. Ignition switch and pig tail are new.
Upon doing some further checking. after jerking off the negative cable, to stop the starter from cranking. I discovered,with a 12v test light,one on the battery negative. Anything metal under the hood i touch will light the test light. Inner fender well,intake manifold,basically,whatever i touch causes the light to come on.
It is also a intermitenet problem. It does not happen everytime you start,may start fine 20 times,then the process repaets itself.
any ideas or thoughts would be great!!