is it in the rear spoiler? Thru the trunk, light socket is right below rear window
I think the light assembly screws out from the inside of the trunk.
Should have an access panel inside trunk
power = light green ground = black
Open the trunk, there should be some long and short screws with nuts on them right above your head. If you have a deep well socket (recommended), you just have to take the nuts off. Then slowly lower the trunk making sure the light assembly stays on the car. Take it off and you should have access to all the lights.
You must remove the entire tailight panel - remove trunk liner and the recessed nuts.
I believe that one is accessed thru the trunk; lift the carpet out of the way and you should be able to remove the assembly.
Trunk light switch is part of the trunk light socket assembly...
To change the third stop light bulb on a 2005 Buick LaCrosse, begin by opening the trunk and removing the cover panel located at the rear of the trunk, which may require unscrewing a few screws or clips. Once the panel is removed, locate the third brake light assembly, twist the socket counterclockwise to release it, and then pull out the old bulb. Replace it with a new bulb, reinsert the socket, and secure everything back in place before closing the trunk.
There is a switch by the trunk lid and sounds like it needs replacing.
To replace the rear turn signal bulb on a 2012 Buick Regal, start by opening the trunk and removing the trunk liner or access panel to reach the tail light assembly. Locate the tail light housing and twist the bulb socket counterclockwise to remove it. Pull out the old bulb and insert a new bulb, then reassemble the socket and the tail light housing. Finally, test the new bulb to ensure it’s functioning correctly before closing the trunk.
Immidiately to the left of the steering wheel, below the traction control switch/twilight sentinel/interior light dimmer controls. Note that the trunk button can be disabled by a switch in the glove box or another switch in the trunk on the locking mechanism itself.