My two cents.....

Your car came with a radio like this. You say you have the fader switch and that is good. I am guessing it is installed in the dash somewhere. This is the hardest thing to install if you don't have one in there now.

But installing the radio is easy. the long gray wire will plug into a seven hole plug in the amp and then the plug into the amp is help in place by a small wire clip.

Look behind your glove box. This is usually where the amps on 108's were placed. It is held into the car by being snapping into a bracket. If you need to see how this works just check out a few amps for sale on eBay. It is simple once you see what you are supposed to be looking at.

It helps to snap the amp out of the mount in order to plug in the wires. The mount is held in place by two screws that are screwed into something solid.

Look at the amp and you will see a black and a white plug that are usually covered by a small metal tab. These are where the speaker wires plug into. The other two small electrical blades are for the power antenna which you might not have on a 108. They were very expensive and during the era were considered not truly necessary. So few customers bought them and few dealers were willing to install them as an installation require removing the inner fender on the right side to gain access to the antenna mounting area.

And more questions just feel free to ask.

Do you have the mounting stalks that are used to secure the radio into the dash?