Truck will start when key is turned to on position, starter stays on after start

IF the starter engages when the key is turned to the 'ON' position without turning it all the way to start.... and will then disengage when key is turned OFF ... Adjust or Replace the ignition switch, down there under the dash on steering column!!!... Do NOT let it run in this condition! Either fix it or tow to have it fixed!!!!.... Any work done on this vehicle right before this problem??... Is your question worthy of an answer in the first place?????.. NO reply will confirm that it is not!!!

What does it do if you turn the key to the 'crank/start' position?

stuck solenoid?