1995 Ford F250 ignition switch

Thanks for the super quick response. I should have told you the problem. When I try to start the truck the ignition stays on and won't turn off from the switch. I know the fords use a relay under the hood and a resistance measure ment should clear up a shorted condition. I thought it was in the key switch.
How is tjhe electrical half of the switch replaced? I smelled something burning. Could the solenoid on the starter be shorted ? how would I check this? Tell me if I'm right, The switch is only a means of supplying voltage to the relay under the hood, the relay closes and suplies voltage to the starter, when the key is released the relay drops out.
This is a diesel engine.


Thanks again,
Rickey