Before doing this, purchase the listed parts from WalMart. My parts cost me around $30, but I bought more than I needed, because I wasn't sure what I needed.
This is easy, but time consuming. The 8 track is secured by 3 items: the nuts on the shafts, a bracket in the back (most for grounder) and the wires. The first thing to do is take the nuts of the two shafts (what the knobs are on). Pull the knobs off, use a socket wrench on the nuts. This is tricky because the nuts are EXTREMELY flat. I think the socket size was around 10-12 mm. The bracket on the back was easy, something like 1 screw. Push the 8 track back, into the dash. You should be able to slip it out the bottom. On the Mark V, there are braches on the underside of the dash, supporting it. Remove 1 to get the 8 track to dangle onto the floor. The 8 track is hard wired in. Slice the wires. There are two groups of wires, one group of 5 (4 speaker wires, plus a common ground for the speakers) plus a group of two (power and possibly a ground wires, or a second power wire). Get some electrical tape over the 2 power wires, you don't want to get a nasty shock later on. If you want, you can get the wires really out of the way at this point. If you follow both groups, you find that they are connected by clips. Disconnect the wire groups. Now they won't be in the way anymore. Pull the antenna wire out as well. You'll want it to be able to listen to the radio (no fear, Ford uses a standard antenna connector that will fit modern receivers).
You'll need the following to do this: socket wrench, Phillips head screwdriver (No. 2 recommended), and a small flathead screwdriver with a sturdy handle. In addition, a piece of wire. I don't know how to describe this. Ever have a dog? Remember the plastic coated, braided wire (about 1/4" diameter, not including the plastic) that you would use to tie him up in the backyard? You'll need about 4-6 feet of this stuff. Open the windows all of the way. Open the doors. Take them apart in the following order (I hope I'm remembering this right):
Take out the old speakers. Unscrew them, unclip the wires from their clip, or slice them. Your choice. You may have to pry them from the door (there seems to be some sort of adhesive on them). This is what your flathead screwdriver is for. Next, you'll need to provide a path to feed the new wires (trust me, you can use the old wiring, but since the speakers probably came with wire, and its inexpensive to buy new wire, you'll want to do this). There is a panel at the bottom of the door jamb, by where your feet would be. Remove this. There are 2 screws holding it in, one near the top, inside the door, and one on the side in the jamb. It will be tucked under the trim in the upper half of the jamb and under the metal "Mark V" plate on the floor part of the jamb. You might have to pull up the metal plate by taking out 1 or 2 screws to get the "kicker panel" out. Don't put in back in yet. In fact, take it out completely. Now this is the hard part. Run the wire through the door. Between the door and the car there is a rubber hose, where all the other wires run through. Tie your new wire to the plastic coated wire. Push it through the hose. When you get through, untie it from the plastic wire, and pull the rest most of it through. Screw in the new speaker (you'll probably have to use the screws from the original speakers). Connect the speaker wires to the new speaker. Pull the speaker wire through the hose, into the car, to take up most of the slack. Lave about 6 inches still in the door as slack (this is for when the door is shut). Tuck the extra under the window. You don't want it to get caught on the window. Put the door back together.
Take out the old speakers. Run the wire (you'll probably need to buy wire, 50 feet is available at WalMart for about $4) through the back of the car. Remove the bottom of the back seat (lift the front up and pull forwards). Run the wire under it. Life the carpet up, run the wire under it, and along the door area. Take up the slack. Screw the metal plate back in to lock the carpet back down.
This step is where you will want to proceed slowly. Measure twice, cut once (you won't get a second chance!). Learn from my mistakes. The dashboard section where the 8 track was is subdivided. There's a "gutter," a silver perimeter, the "wooden" panel, and the hole. Get the dimensions of the silver perimeter. I think it's something like 8"X3". I don't remember. Measure your new stereo precisely. Put the Tupperware or Rubbermaid lid on it's container, for support. Using a ruler or a template, mark lines so that it will match the size of the silver perimeter on the dash. Make sure you draw lines, not simply mark beginning and ending points. You want this to be PERFECT. Mark, again with lines, not dots, the hole for the stereo. Center it precisely. Using a drill bit a tad bigger than the blade for the electric jig saw, drill the inside of each corner of the lines for the stereo. Drill on the outside of the lines at each corner for the entire piece. Drill out the hold for the stereo. Make sure that the stereo fits snugly into this hole before proceeding. If it won't fit, use the file or the saw to open the hole more. If its loose (more than an extra 1/8" or so) make a new one. This is the most visible part of this job. Don't screw up. Cut the entire piece out. This is your new faceplate. Use the wood file to make the edges perfect. Some receivers come with a little plastic "ring" to go around the front of the receiver to give it a nice look. If yours has this, don't bother making the hole in the faceplate too pretty. Now's the time to make your faceplace pretty. Contact paper, spray paint, whatever you want, so long as its something you're happy with. I left mine stock white, but I'm pretty sure I'll pull it off and paint it flat black, or maybe maroon to match the interior.
Most receivers come with a wiring "squid" that you will supposedly be able to get a harness for for quick connection. Forget able finding a harness, I tried. Strip the ends of the wires on the squid. Crimp your connectors onto each wire of the squid. Most receives today have 3 wires for power: red for "accessory/ignition" power, yellow for "always on power" and black for ground. Strip and crimp the appropriate wires that you bought onto these. In the car, strip and crimp the speaker wires to the appropriate wires on the squid. some stereo and speaker combinations (Pioneer for example) have special connectors that don't use a squid. In that case, leave the existing connectors and use those, or splice them back in if you have to extend the wires for the rear speakers with store bought wire. To establish the ground, you will need a good ground point. In the Mark V, there is a small ground point on the floor near the racing black, with a wire or two already grounded there. This area is under the kick panel which you removed to to run the speaker wire through. Ground to this area. Don't forget to strip the end or the wire. You'll probably need to use the small washer here to smoosh the ground wire in. For the red power wire, pull the fuse for the radio/antenna (number 2 or 3, I think). It's underneath the flasher component, which pulls out. Put the wire (strip the ends). where the fuse was, and put the fuse back in, so that the fuse holds the wire in. You may want to spot solder the wire in. Do the same for the yellow wire, but on a different fuse, one that is for "always on" power and rated at the amperage for your receiver (I used the clock/dome light fuse). Tuck the slack under the carpet. Make it look nice, make sure that no wires are near the pedals. do the same for the speaker wires. Your wires are ready.
"Tack" the faceplate onto the dash using Liquid Nails. Make sure it looks nice. If it doesn't, move it or pull it. Make a new faceplate if it doesn't sit right (the silver perimeter should be completely visible, but nothing inside of it). Using a small drill bit (smaller than the small screws you bought), drill a hole in each corner of the faceplace and into the dash. Screw the faceplate onto the dash. Here is the step where if you screw up, you'll be miserable and unhappy. Using the electric jigsaw, trace the outline of the hole for the receiver. Make sure you do not cut into the faceplate. Make sure you follow it exactly. Go slow. Cut both the dash and the tick, hard plastic behind it. It will produce an awful smell, and you may be close to overheating the saw. Go slow. DO NOT CUT ANY OF THE WIRES BACK THERE!!! Take all turns slowly and obliquely. Once you cut the corners round, you can cut them and square them with you're done with the cutting. Use the file to remove any obscene "hangers" and shreds of plastic. Make sure that the receiver fits snugly in. Duck your head under the dash. You will see the area for the ashtray. There will be a "ledge." Between the ledge and the upper, vertical part, there is a huge python of wires. In line with the light of the ashtray (the light is centered for the hole), behind the ashtray and it's mounts, but right in front of the python, drill a hole slightly smaller than the screws that came with the corner brace. Go through both layers of plastic. Inside the area for the receiver, screw in the corner brace. Use only 1 screw (you won't have room for two). Mount it so that the vertical part of the L is pointed up, and the the corner sits on the edge. What I'm saying is maount it away from you. Otherwise, you won't have enough room for the receiver, and it will stick out 2 extra inches. Slide the receiver in. Locate the hold in the back of the receiver for the metal strap they gave you. Using the screw it came with, screw the corner brace into this hole. Make sure that the stereo is square and even. Move the brace if you need to. If all went well, it will look great, and be sturdier than any kit you could have bought at the store (mine looks good, at least). Attach the squid to the receiver. Attach the antenna wire. Reconnect the battery, make sure everything works. Reinstall the brace for the dash now. Reattach anything else you may have taken out.
And that's it! I know this sounds confusing and complicated. follow the directions step-by-step, and you'll be fine. I had to figure this out, and it came out fine on the first try.
Credits: B.J. Richards provided tremendous amounts of help with the doors and selecting the components for the faceplate and installation. Phil Priest, my roommate, told me how to do the rear speakers.
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