1995 GMC Jimmy brake lights

No, not the brake-switch. The lower brake lites are wired through the multifunction switch, the high-mount brake lite isn't, they both get voltage from the same brake switch, the routing is different. The lower brake lites and turn signals use the same bulb filament, just not at the same time. The problem is probably the multifunction switch or wiring in the steering column. Any fuses that you checked, did you use a voltage tester to see if circuit is hot? Do the turn signals work ok? I can give some wiring colors if you want to do more testing?

turn signals work but also the emergency flashers do not checked flasher relay beside ciarette lighter it is good