Brake Lights

Chevy Limina 1998, 3.1 1,500,000mi. The break light system is acting up. The third light in the rear window works all the time. No Problem. The tail break light dont work. I replaced the break switch twice. When the switch is out but connected the break lights stay on no mater if the plunger is depresed or not. When the switch is secured into the housing the break lights dont iluminate at all. All the bulbs are good. All fuzes are good. I hear a relay under the dash that when the plunger is depressed it makes a loud click. Noticeable becuse my head is under the dash. HELP