Having a really tough time wrapping my head around this starter problem. I have a 89' f250 4.9L that after being turned on the starter will not disengage from the fly wheel. I have already replaced the starter, replaced the ignition switch, and the starter solenoid. I thought it might have been a problem with the solenoid however i jumped it over and the starter still will not disengage. If anyone has a clue what might be going on with this thing please help.
Thank You

 

You've pretty much replaced everything in the circuit, so the only thing left is a short in the wiring....