lightning wont start
 

I went to start my truck today to run some errands and it wouldnt start.It would just click like when you have a bad or dirty connection.So I opened the hood and saw the battery posts were corroded so I took them off and cleaned them.Then I checked the battery on a charger and it was fine so I tried it again same thing.After this I crawled underneath and removed the ground and connections to the starter and cleaned them with a wire brush.None of these things helped.Is there a way for me to tell if the starter is shot before I take it to a garage?The closest ford shop is 100 miles away.Any other ideas to what it might be?