These are the steps i take to remove the original radio and install an aftermarket deck.
Things You Will Need
Ford radio removal tool. Aftermarket dash kit and harness. Wire strippers and crimpers. Panel tool remover.
The radio for this car is in the trunk. The controls on the dash are what people most likely assume is the radio. The radio is on the drivers side rear fender well. This is where we will be attaching the harness that will need to find its way to the dash where the new radio will end up. Remove the false floor of the trunk that covers the spare tire. Sometimes there is enough of a gap to get to the harness and antenna lead underneath the side interior trunk panel to be able to unplug the harness. If not, you will need to remove the panel completely. It's held in with a few clips that are very visible. Once you have it off you will see the radio and the plugs you will need to unplug.
The next thing i do is make all the connections i need. Most of the kits for these cars come with the needed harness with the length to reach where the new radio will reside. You will need to run the harness under the rear folding seat, and along the floor of the car. Remove the plastic door sill plate with a panel removal tool. They come off by unclipping them straight up off the car. Once you have them off, you will be able to tuck the harness underneath the carpet. Run the harness up to the kickpanel, and zip tie it to existing cables in the car. Try and route it the best way you can so that you see the least amount of wire, but make sure you have enough to make it to the dash where the radio will go.
Now you need to remove the dash control unit. You will see four small holes in the panel. This is where you need the ford removal tools. These can be purchased at most auto parts stores for a few dollars. Push the tools in each side until they click in, and push outward on each side and pull the radio out of the dash. Once you unplug all the harnesses, you can remove this from the car. Now you can finish running the harness to the open hole in the dash. I usually zip tie the harness to one of the harnesses i unplugged so it stays in place. Now you can wire up the plug for the new radio. Most of the time it will match up color for color.
Next, you will be transfering the climate control electronics to the new dash kit. They are each held on by one screw. The control knobs are pressure fit and slide straight off the front. You will also be transfering the retaining brackets off each side of the old panel to the new kit. Now you will be plugging all the harnesses back in. Click the new kit back in the dash. Make sure it's all the way in on both sides. You will have disconnected and reconnected vacuum lines, so they won't get pressure back until you start the car back up. Make sure all the climate controls are functioning the way they should be. Now you can slide the metal cage that came with your new deck into the opening, and secure it in place by bending the proper tabs. Plug the harness and antenna lead into the new radio, and slide it into the cage until it locks in. If you have not already put panels of the car that you needed to remove earlier back in place, that's all you have left to do.
I hope this has helped out. This is definately a unique car when swapping a radio out. The order of the steps i take can obviously be changed, but this is how i feel comfortable doing these cars. I am a 12 year veteran mecp certified installer.
Tips & Warnings
This is not a car i would recommend doing with little to no experience. If you don't feel comfortable with it, please let a professional do it for you. Replacing original parts can be expensive.