1995 Buick Regal breaklights

I'd start by checking applicable fuses and bulbs. Tail-lamps get voltage from the headlamp switch. Your lower brake lites and turn signal at the rear, use the same bulb filament, just not at the same time. Dual filament bulbs, one filament for tail, the other for stop/turn. I'd check for voltage and ground at the lite wiring.