Ford Repair: battery good but sometimes wont turn over, ford rangers, voltage drop

Question
I have a 1991 ford s10 that will start most of the time, but sometimes I try to start it and all it does is click and wont turn over. I had the battery checked and it tested good. I tightened the connections and the ground wire. it started fine for a few days then didn't. I can jump it and it cranks right over. Any ideas?

Answer
i know you have checked them but-connections/bad cell in battery or starter-can't be more specific because ford don't have an s-10 and s-10 and ford rangers have different starter setups. but either way it should be same problem as mentioned above you may have to run voltage drop across cable if you don't know how to do this take it to a reputable garage-you may be surprised how much money you may save by not slapping on suspicious parts. and having it diagnosed properly instead. good luck.