I remember Buick sedans of the 1960s had tail lights that extended the whole width of the car. I always liked this look-what model years used it?
65 Skylarks and 66 to 68 Electras and Wildcats. Some later 60’s Riviera had full width tail lights except for the license plate area. None of these were as stylish at those used on the 66 and 67 Dodge Charger or the 67 and 68 Mercury Cougars.
1985 to 1987 Buick Somersets also had them. Somersets were the Buick Grand Am in those years. Later models were Skylarks, and at least some of them had full width tail lights.
Cougar tail lights had sequential turn signals (like some T-birds) that were run with a motor and camshaft affair.