Will it fit?
 

Will s5 tail lights fit my 87 FC?

simply..YES.
But you have to cut a small piece of metal the car to get the tails to fit...around the 2nd light bulb area(close to the reverse light)..about the size of a 2 inch square(give or take),as the bulb may hit the metal.You can either cut or bend it back to get them to sit flush.
Use the harness that the s5 tails came with.
There are numerous threads that show you how to do that,so for that aspect you can find out any info on this by merely searching and cruising the Sec Gen specific section.

Awesome thanks