1996 Buick Century tail lights

You should be able to access the tail light assembly by going into the trunk, removing the wing nuts or bolts that hold the cover will expose the assembly; it may be necessary to remove the bolts holding the assembly to the body if it is not secured by the bolts that you have already loosen. Be careful as the retainers are probably plastic, if one breaks, then water will come inside light assembly/trunk and you will have a problem.