Do you have a brake light switch on this car mounted off of the brake pedal? I am not familiar with the 700 series but it probably has the switch mounted somewhere so that when you step on the pedal it lets a little button move out and thus close the circuit and turn on the brake lights and then when the brake pedal is released it pushes the little button back in and turns the lights off. If you have that setup check to see if it has become jammed or something and the switch itself may be bad.
The other thing to check first would be to see if you are getting power to the wiring harness in the trunk before it goes to the lights.