I can help you I had that problem on my 1988 cutlass ciera and the answer is that one of the lights on the back not the third small on is not working. Open the trunk take out the bulb itself and check the wiring. That what was wrong with mine someone didn't have it wired right. Hope this helps you out.
Stuck brake light switch.
Check the brake light switch. It's under the dash, connected to the brake pedal. If it's adjusted wrong or faulty, it could cause the brake lights to stay on. If you can use a meter and tell that the brake light switch is ok, next test the turn signal switch. Sometimes they short out and leave the brake lights on. You'll have to pull the steering wheel to do that.
If the tail lights were hot during the swap you may have broken the filiments. Bumping a bulb that is on or been on recently can cause the filiments to fail. Remove the bulbs hold them up to a light and see if the filimant is intact.
fuse, bulbs
brake light switch would be most common cause
It's probably your'e brake light switch sticking ,i think it's down under the brake pedal connected to the pedal try pulling up on pedal , check switch,unplug it see if lights go out
BAD BRAKE LIGHT SWITCH AT TOP OF BRAKE PEDAL
The BOO (Brake On/Off) Switch may need to be replaced. If it is bad, it would cause the brake lights to NOT illuminate when the brake pedal is applied.
Possible ground issue at the taillights.
Blown fuse or defective brake light switch.
Most likely a fuse.
The most probable cause is that the brake light switch is out of adjustment.