1991 chevrolet s10 blazer blinking warning break light?

my chevrolet s10 tail lights and reverse lights are not turning on and the warning break light is now blinking in the dashboard. i bought a fuse tester and i test everysingle one and they all work, i also replace the bulbs to see if that did but they still don't turn on. there is nothing wrong with the breaks or the emergency break, everything works as it suppost to except the tail light and reverse light. weird thing is that if you know the gms they have a break light tail light and reverse light. the break light works but the other two don't anybody knows whats going on or some tips let me know thanks