Remove the taillights by removing the 6 long screws. I recommend using a Phillips screwdriver, not an electrical screwdriver, as turning in the wrong direction, or over-tighting these screws, will break the tabs off of the housing that holds the clips. With the taillight assembly removed, now is a good time to disassemble and clean the lenses. Make sure the assembly is warm. I placed mine near a heater to warm them to ensure that I did not break any tabs during disassembly.
Once the unit is warm, lift up on the 6 tabs. Be gentle, do not force, and the back will lift off. There is a clay-like sealent around the edge, leave this on so it will seal when you put it back together. With the back removed you can now wash the pieces, and on the clear outer lens you can remove any scraches and nicks. I used fine sand paper (1000 & 1500 grit) and then auto polish to remove the scratches.
I ordered my LED's from Top Line Group Automotive. They have a complete package for the Fiero. The parking LEDs are the same for all models but make sure you get the correct ones for the tail lamps as the coupe is different from the fastback. The rear lamps come complete with a new flasher unit and load resistors. When I removed the LEDs from the package I used a felt pen and placed a "R," "W," or "Y" for the color so I would not get them mixed up.
The flasher on the right is the one supplied by TLG. If you use this flasher you must install the load resistors, (1 on each side of the rear turn signal wiring). I did not want to install the load resistors because I was tying to cut down on the load on the battery. I did a search on "led turn siginal flasher" and found the unit on the left. It was from eBay, the part is United Pacific part number 90650. I do belive any of the 2-pin flashers with the wire coming out of the top, (this is a groung wire), will work. Make sure the flasher states "LED compatable." Do not throw the TGL flasher away, remove the Hazard flasher and replace it with the TLG unit.
When I tried to install the LEDs, I found them hard to seat into the white sockets. I had to take an X-acto knife and bevel the edge just a little. Make sure the new LEDs are well-seated.
Now that you have all the LEDs installed, test all the systems. I had one LED that worked well before I put it into the taillight assembly, but it would not flash when installed in the assembly. It was not seated correctly. I did not say anything about the parking lamp assembly. They are easy to do, the one decision you need to make is to use the clear lens supplied by TLG or reuse your OEM yellow ones. I chose to use the clear ones, it gives the car an updated look, in my opinion. Enjoy.