1995 Buick Regal brake wiring

Welcome, does the right turn signal at the rear, work? The lower brake lites and turn use the same bulb filament, just not at the same time. The dark green wire carries voltage for that circuit. Right now, my guess is a faulty turn signal switch? There may be a multiwire connector under the dash, close to steering coulmn. You might be able to test dark green wire at that connector. If voltage there and not at the rear, problem with wiring circuit. If no voltage at connector, with brake applied, either the wiring in the steering column or turn switch. All repair info, says to disarm the air-bag, where applicable, when working aroung the column.