Brake light question

I have a 1991 Honda Accord LX, 157,000 miles, automatic. Problems with my rear brake lights. When pressing the brake pedal the rear lights won't come on and then sometimes they do. I was looking for a fuse to test from and to but couldn't find it. I have rear lights when turned on as well as back up lights. The bulbs have been tested and are good. Where do the wires come from go get to the rear brake lights? Need help in point right directions to look for problem. Since it is intermintent I suspect an open in the wiring but I don't know where to look.