Brake Light Stays On

Not sure if this is the same issue as with mine. I have a 1999 automatic sedan:

http://www.justanswer.com/car/02niq-1999-ford-mustang-v6-automatic-the-shifter-gets-stuck-park.html

I was talking to a transmission mechanic (he rebuilt and installed my automatic for me) and he said that the brake lights aren't working at all.

When I get the car back, I will want to check (1) the fuses (2) the bulbs (3) check for power at the rear lights when the pedal is depressed and (4) the brake pedal sensor / actuator that detects pedal depress which unlocks the transmission (this is likely the problem on my car)

In your case, it's more likely that either the pedal switch is bad, OR there is a short in the system.

Do the lights stay on with the key OFF?

Good luck.