1994 Mercury Tracer Engine won't turn off

We got an old Mercury Tracer for my daughter to drive around as a first car. We have had it for about a year and she has put about 6000 miles on it. Now the engine will not turn off. The only way to stop it is to pull the engine fuse. When you put the fuse back in, all the warning lights on the dash go on. When you turn on the engine, random items don't work: sometimes the radio, sometimes the heater, sometimes the headlights are dim. It has died once while shifting from reverse through neutral and once it wouldn't start until I shifted through the entire range of gears a couple of times.

Shorted ignition switch, maybe? A faulty safety switch? Any help would be wonderful.