brake lights 98 gmc 1/2 ton

[98bikerman]

I am having brakelight problems on my 98 Gmc pickup. The lights started out just making a quick flash when the brake peddle was pressed then the lights would go out. I have checked all fuses that I know of, check all bulbs, replaced the brake switch under the brake peddle , and now have changed the brake lamp relay under the hood. I now get not lights from the brakes. I have all others turn signals, hazzards, headlights, parking lights all these work. CAN ANYONE HELP WITH MESS