My rear brake lights and turn signals are not working - 2002 Buick Regal LS?

The front signals are working fine, and there is a brake light on top of the truck at the bottom of the rear window that is working. The rear lights all work fine, but the turn signal and brake lights are not responding. I have ruled out wiring and fuse problems, all are in proper working order. Any help would... show more The front signals are working fine, and there is a brake light on top of the truck at the bottom of the rear window that is working. The rear lights all work fine, but the turn signal and brake lights are not responding. I have ruled out wiring and fuse problems, all are in proper working order. Any help would be greatly appreciated.
Update: there are 4 total bulbs on the rear of the car. 2 for turn signal/running lamps and 2 for brake lights/running lamps. Each bulb has 2 separate filaments for each function. I find it unlikely that 4 filaments would have gone out at the same time, but I will check them today.
Update 2: oh, forgot to mention the bulbs still work for 'running lamp' purposes.
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