Pontiac Problems? Ask a Mechanic for Answers ASAP
Hello and welcome to JustAnswer.
My name is Vlad.
Based on your description of the problem, it sounds like you have a bad ground issue.
All rear lights share the same ground G400 so you will need to make sure it is tight and clean. It should be attached somewhere near the rear compartment lid lock release actuator.
Please let me know how it goes.