85 mustang 5.0 cranking in run position

Recently had a starter go bad on my 85 mustang. Its a 5.0 5 speed, carbureted with duraspark ignition. Replaced my starter and later found i also had a wiring issue that was causing a voltage drop. Fixed that issue and now having a problem when i turn the key to run position the car cranks over. Assumed bad solenoid but i had a spare known good part that I replaced it with, still having same problem. Any ideas where to look? Was after replacing ignition switch last year with a motorcraft replacement. Confirmed good battery, verified grounds. Could it be the tumbler itself? TIA
 
Remove the ignition switch, reconnect the wiring harness to the switch and manually work the ignition switch. If it still tries to start in the run position I would suspect the switch.