1997 Mercury Sable electrical

I am having electrical issues with my recently purchased wonderful 1997 Mercury Sable Wagon.

The problems are all intermittent except for item 1 below.

1. If the car is on and the lights re on, the rear defrost light on the dashboard goes on and cannot be turned off.
If that was all I wouldn't care, but read on.

2. The overhead light on the ceiling of the car sometimes cannot be turned off so I simply take the bulb out, again, no big deal

3. Sometimes the radio won't go on, sometimes it goes on but the volume cannot be controlled. Not a big deal BUT sometimes it won't go off, even with car off and key out and even if I remove the two fuses that relate to the radio. I had to disconnect the battery cable to get it to go off.

4. Sometimes the light on the dashboard shows that there's a door that's not fully closed, even when all four and the trunk are 100% closed.

5. A couple of times the headlights have not gone off even with the car off and key removed.

6. Last - sometimes the windshield wipers, turned to go fast in a heavy downpour will go fast for a while and then go slow for a couple of minutes and then go fast again.

I am pretty ignorant where it come to automobiles (my expertise is wood) but I'm speculating that all these things are connected at some ISO relay or some relay switch where perhaps the solder is failing.

This is a car I gave to my wonderful daughter in South Beach in Miami and I'd love to be the hero by identifying with your help the solution.

Thanks,

Kerry