No brake lights?

I don't have brake lights when I step on the brake pedal. I have turn signals and parking lights. I checked the fuses and they are good. There is only one wire to the brake switch and looks like it works off a negative ground type setup? I think it works when you press the brake pedal, it completes the ground, but not sure. Can anyone tell me how to test for this to get them working again?
Thank you,

John....
Author: 66sportfury