Reconnecting battery/starter issue

Okay, so I have a 95 YJ. A few months ago it wouldn't start, I could hear an audible click but the starter motor wouldn't actually try to turn the engine over. Did some research, and determined that either the starter motor was out or wasn't drawing enough current. Replaced the battery and the starter motor, didn't work still. Finally, I replaced the lead from the battery to the starter, and that did the trick.

Flash forward to this morning, I go to start my Jeep and the same issue is occurring. I immediately go to check the connections. Turns out the connection from the lead to the starter motor had come loose. Just a small jiggle of the lead caused it to pop off, with a little bit of sparking. So I go ahead and disconnect the battery, then reconnect the lead to the starter motor. I go back to reconnect the battery. Start with positive terminal, get it hooked up. When I go to attach the negative terminal, I slip the connector over the terminal and hear the starter motor crank...it doesn't turn over the engine but cranks a few times before stopping, and after that I just hear something whirring, like a motor running or something. Freaking out I reach for my pockets and verify that my keys are in fact in them.

Can anyone explain what is going on? I haven't messed with it since for fear of blowing out something. Thanks.