I am sure I will have to figure this one on my own. 2003 Express 3500 6.0l With key in off position starter is cranking. However in crank position starter is silent. There power there. Also power in run position. If starter relay is pulled starter is completely disabled. I can make engine run by jumpering starter at small terminal on starter. Then pull starter relay so i can shut it down. All fuses good. New relay from GM. If ignition switch is unplugged, starter will still crank engine as long as starter relay is plugged in. I will keep everyone up to date with this. I am thinking I have a wire that may have melted in harness and has connected with something that it should not be tied with. Puzzling how starter will only crank with key in off position ??? No crank in run or crank positions, unless I bypass at starter small terminal. All fuses good. Time to hunt....