Now here's where my instructions may start to get foggy. Just ask if I make no sense. I noticed that you have an 87 GT. I have no idea if this is possible on the other body style.
Take the right rear wheel tub off of your Fiero. Also remove the assembly that houses your side rear marker light (the red one). You will see that the rear panel has a fiberglass reinforcement that is about 1" to 1 1/2" above the hole where the light bulb socket went through the body panel. This thing runs all the way to the door, and there is probably something similar in front of the door too.
Just to the front of where that light bulb socket goes throught the car's body, on that piece of fiberglass reinforcement, you will see a oval shaped hole. I mounted the antenna through that hole, and up through the body at a point directly above that hole.
I installed the Nissan piece by cutting away the right shape in the car's body, including two extra holes to stabilize the Nissan thing, and to keep it from rotating. The part has two pins sticking out of it for this purpose. The part is held to the Nissan 300 by a bolt that sticks out of the back of it, through a hole, and is held with a nut. You will find that in order to use this existing bolt through the fiberglass reinforcment on the Fiero, you will have to lengthen the bolt. I did this by using a second nut and a second bolt with the same threads, and joining the two bolts together with this nut (half of the nut on each bolt) with some lock-tight.
The antenna I used is the aftermarket kind you can find anywhere for $30.00 or so. I got mine at Auto Zone, but I've seen the same antenna, marketed under a different name, in K-Mart too.
I secured the antenna in two places. I ran a piece of 1" x 1/4" aluminium from the bottom of the antenna (there are holes here for this purpose) to a very convenient point in the brace that holes the rear bumper on. There's already a hole there to mount the other end of the aluminium. The second place where I secured the antenna is bit harder to explain. There is a piece of metal which runs between the upper and lower body parts right under the red side marker light. This is the piece that has threaded holes in it to hold the side marker to the car, and two hold the two body parts together. It is rivited to the car. I drilled through the rivits, removed the piece, and created a new one that is a bit longer. With this extra length I bent the new piece of metal so that it could run over the antenna shaft, thus holding it to the car's body.
You will have to have constant power to the antenna, so that it will be able to go down when you turn the key off. I got this power from the trunk light wire. I ran the coax and the other wire that goes to the radio up over the wheel tub, and back down the front side of the tub, then through the lower rocker panel (I used a plumber's snake to do this), and finally ran them through the grommet where the original antenna's coax entered the car.
My Kenwood Stereo is not set up to lower the antenna while I'm listening to tapes, so I also installed a cut-off switch to the left of the center vents. One of those nice lighted rocker switches will fit right in there.
I painted the Nissan thing black, but I will have it painted the same color as the car when I get rich enough to paint the car. At that point, I will also have the original antenna hole filled in and painted, too. For now I just put a rubber cap over that hole, but I don't think I had to do so. It just looks a little better for the time being.
I hope this helps you or anyone else who thinks the the Fiero deserves a rear-mounted power antenna.
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