First, go get the OM -> https://www.fleet.ford.com/maintenan...ls/default.asp
Next, what you're describing sounds like the current the Starter requires isn't getting to it. The next observation you should make is what happens to those lights on the dash when you roll the key to start. Do they dim? You can also turn the Headlights on and watch them when you try to see if they dim.
If they do, the entire system is having trouble supplying the current (bad batteries - connections ANYWHERE in the cables, or the starter itself is asking too much because it's bad)
If they don't, the click you hear is likely to be from the starter solenoid (pass tire well under the hood) or the starters Bendix solenoid that throws-out the gear and mounted on top. Sometimes the starter itself has a bad connection inside where the brushes ride on the commutator.
The first, and easiest thing, to do would be to slide-under with a hammer and give the starter a few whacks. This often reseats the Bendix/Brushes and the starter will work. Carry a hammer with you and see if it fixes it a few times then I'd be thinking Starter.
Next, is the solenoid on the fender well. It has two sm wires going to it and two lg. It's job is to connect those large wires together when you turn the key (activated by the two sm ones) and send Big Power to the Starter. With 1/2 a jumper cable (just one side) you can jump those two big wires and bypass the solenoid. If it cranks-up fine (and the "click" you hear is coming from it) I'd be thinking it's bad...