replace ignition switch
with a spare key
Ensure alternator is functioning properly.
Its a Ford self test. Key On Engine Running. There's also the Key On Engine Off.
Did they used to go off with the ignition? On most cars, the headlights will come on at any time by just turning them on. The car does not need to be running or the key turned on.
If it starts but doesn't stay running after you release the key from the start position, it means your ignition switch is bad. Not a huge expense.
The 1991 Ford Explorer should have a separate starter relay that sends power to the starter. It sounds like the relay has stuck and is sending power to the starter even after the vehicle is running.
Probably a bad relay.
Could be defective stater solenoid that is not releasing
the pad is right on the driver side of the door
I am not sure of the entire problem whether it starts all the time and stalls occasionally or does it shut off as if you just turned the key off? If it is the latter, check the ignition module near the distributor. If it is running try tapping the module and if it stops, that may be your problem.
ckeck the solenoid on the passanger side front fender
neutral safety switch is messed up