I have a 1991 Mercury Grand Marquis with no brake lights.have checked all fuses still no lights

I`m guessing that the signal lights work,there fore the brake light switch is probably the problem.it is located at the base of the brake pedal and pushes the switch when the pedal is moved.there is two wires for the brake lights on the switch one wire has power all the time the other wire only has power on it when the pedal is pushed.check with a test light for power to these wires at the proper time.also check and make sure the wires are not broken as this is also a problem with this system.