1992 Mercury Tracer Starter Problems

Recently, my vehicle starter on my 1992 Mercury Tracer will continually crank over in Park and Neutral without the key in the vehicle or in the "Run" position. As a temporary measure, I have been forced to leave the vehicle in "D", "L1", or "L2" when I shut off and park it. In order to start the vehicle, I turn the key to "Run" and quickly shift the vehicle into Neutral then "D", until the engine engages (if I leave it in Neutral, I hear a loud grinding noise, which I suspect to be caused from contact with the flywheel as the starter is not disengaging and is continually running). I use the same method when starting the vehicle from Park and I am forced to quickly move the shifter to Reverse or the same problem happens as mentioned previously. Your insight and reccomendations would be greatly appreciated. Thank you in advance.