Issue with rear brake lights- intermittently will come w/o brakes being applied.

What is your question?

Bought the car from my dad and this happened to him also. He took it in and they couldn't find a solution. The rear tail lights will come on without pushing on the brakes and then when I do press lightly on the breaks they won't come on. If I apply the brakes hard the break light will come on. Often when this occurs the traction control light comes on also. This is a random problem and it's been difficult for the mechanics to find the problem. Is this a short in the wiring? And if the mechanics can't fix it am I still responsible a bill???