How do I get my headlights to turn off after I shut the ignition off?
Probably the light control module. Common issue. It is above the swing down fuse panel under the dash on the driver side. Swing the panel down and you can slide it back a little and it will release. Replace the module.
Search Buick Century Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Buick Century Experts