How to identify the different box trim packages?

[91merc]

I was wondering if you guys could help me identify the different trim packages on the 79- 91 grand marquis cars

[Tiggie]

From 79-82, there was the base model Marquis, followed by the Marquis Brougham, and the top line Grand Marquis.
83-91 made the jump to "just" Grand Marquis but with a base model (called GS in later models) and upgraded LS with cushier trim.
The original dealership brochures are a great resource for info about what each model had or didn't have as far as standard and optional equipment. This website has a lot of them. https://xr793.com/mercury-1989-1980