Feedback issues

[me@me.com]

I have a 94 Mark 8 that has some ignition issues and I'am wondering if anyone else has any experience with the same thing. The ignition feeds power to the starter selenoid when the key is in the on position, the car will start and run just fine but the only way to stop the starter from engaging is to hold the key all the way to the start position. When the key is turned to off the engine will stop like it is supposed to, I have replaced the key tumbler & ignition switch and nothing seems to help. When checking at the starter with a voltmeter it has power to the ignition wire when the key is in the on position but nothing when in the start position, its almost like the wires have switched places???