I have a 2002 Mercury Mountaineer with a brake light problem.?

It seems that my brake lights stay on constantly, even when the car is off. I have disconnected the brake lights from the pedal and they turn off. If I move the switch down a bit, it operates correctly; however, it takes some pushing of the brake pedal (more than usual) to get the lights to activate. I am trying to avoid a costly repair, and think the switch needs to be replaced. Any thoughts? I appreciate your thoughts in advance.