Starter

I have a 93 ford ranger that runs perfectly fine. One day when I was visiting a friend I parked my truck on a hill for ten minutes. When I went to start it again all I got from the truck when I turned the key is a single mettallic click from the cylinoid on the fender. Within 3 days of sitting the battery died completely. I got another used starter, tested and when it checked good I installed it. I replaced the battery and when I tried to start it again and got the same problem as before. So I change the fender cylinoid with a brand new one. Still the very same problem. When I turn the key the starter tries to work but it seems its not getting enough power. I asked around and the popular cencus is theres a bad ground but I have no idea where to find this mysterious ground. I need help before I send a good vehicle to the scrap yard.