whats the difference and are the compatible

 

I believe they are compatible. The overall shape of the lenses and housing are the same, but onloy the lenses change.

97-90 featured the Firebird logo in the middle around where the rear hatch key hole is.

In 91-92, this Firebird logo vanished and was replaced by either black lens plastic, or by the name "PONTIAC" scrolled across the back.

Here is a pic of my taillights on my 1991. You can see the Pontiac name which replaced the Firebird logo

 

First the reflective red strip is on the bottom on the 85-90's
The turn signal is the two inner red lenses same as the brake lights, not the amber edge ones,and the 91-92's are 2 pieces the the 85-90's are 3.

Personally i like the 85-90's myself and put some into my formula,i do not car for the amber lenses on the ends.

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84 FIREBIRD-(undergoing rebuild)2.8 V6,5spd,T-Top
90 Formula Modded 350 TPI T-Top
WANTED:82-84 Firebird 2.5 4cyl,4spd-Just Cause

Previous 3rd gen's
83 Trans-Am 305 CFI auto T-TOP
84 Firebird 305 H.O. auto HARDTOP
87 Firebird 2.8 V-6 auto HARDTOP

 

so its going to fit though.

 

Yes they will fit any Firebird from 82-92.
although on the base model birds and the Formula's from 86-92 you will have to change the wiring in hte rear.