F250 Ignition Trouble
 

I have a 2002 F250 SuperDuty 4x4. Recently the ignition switch "froze" and would not allow me to crank the vehicle. I can place the vehicle in neutral and then crank, but fear this cannot be healthy!

Any ideas on what to check for repair? I have tried to replace the fuse which controls the steering column, 4x4 switch, etc but the fuse immediately blows?

Thanks.