I have battery cut off switches on all my cars because I have had a car fire, and don't desire to relive that. But in direct answer to your question Rick, try replacing the starter solenoid. Being located right on the inner fender, its an easy five minute swap, and as I recall costs less then $20. My mother had two 1987 TownCars, and both would develop mysterious battery drains after awhile. The starter solenoid became my go-to fix when nothing else seemed to be the cause. Just be sure to disconnect the battery before swapping the solenoid, and yes, that's the voice of experience!
Concerning battery disconnect switches, I am very much an advocate for them, especially after having a car fire, but they are not perpetual. After a few years they develop enough corrosion to impede with starting the car and impede the alternator from properly recharging the battery. This is NOT meant to say don't use one, I'm simply saying that if you install one and after a few years your car isn't starting or charging like it should, check the disconnect switch.