1992 f150 4.9L. 5Speed. The starter keeps trying to Engage while Driving Down the Road. HELP!!!!

 

If I recall correctly, the power signal comes from the ign switch down to the solenoid on the starter. There could 3 reasons that I can think of presently and they are possibly the ign switch assy is defective, the wire at the starter solenoid is too close to the positive battery cable connection at the starter solenoid allowing power to the pull in winding of the solenoid or there could be a broken return spring where the solenoid is mounted on the starter allowing the drive to float around and hit the flywheel.
Something like this can be verified with with a simple test lite connected to the small wire on the solenoid and every time the solenoid gets activated the light lites up and provides a visual picture of the problem if it is caused by an electrical feed. All you do is connect the clip of the test lite on the small terminal and ground the probe point and every time power is supplied to the solenoid you can see it , if that is the problem. You can drive it while doing the check.
You may wind up having to replace the starter if the drive is damaged and if the spring is broken you can see it. Let's hope there is not too much damage to the flywheel or it may need to be replaced also.

 

+1 for ignition switch. Confirm by checking for power out of the switch to the start circuit with the key in run. typically, you will see some voltage leaking into the circuit...maybe not a full 12volt but 8 or so. You may have to check for 10minutes or so to see the voltage.