2000 Ford Explorer • 4.0L V6 4WD Automatic • 104,988 miles

In my explorer, I got in it to go somewhere and turned the ignition to start it and everything went dead like its not getting enough juice from the battery. I checked the battery and it had a full charge, so I cleaned the terminals all the way of the corrosion that was on it, tried again and it started right up. So I go somewhere and go to start it and it doesnt start again, so I mess with the terminals again, clean them again and it starts up, I take it home turn it off, try it again and no start. So as Im getting frustrated I again clean the terminals which by now are crystal clean and it starts, tried it 30 mins later and it starts, tried it again and no start, I can't understand whats going on with it, does it need new connectors or is there another bad ground wire somewhere?
April 13, 2014.

Could be the starter relay or the starter motor itself

Apr 13, 2014.