Toyota Repair: Alternator, battery, or wiring?, 1995 toyota tercel, toyota tercel

Question
Hi there. I have a 1995 Toyota Tercel automatic with 60,000 miles on it. Over the past year, my car has been perfectly fine, except for every once in a while (once every three months) it wouldn't start at all. It seemed like a dead battery, as none of the lights worked, and the ignition made no noise of trying to turn on what so ever. The weird part is, any time this happened, I could pop the hood, wiggle the battery connections, and everything would go back to working just fine. And the battery connections are both very snug.
I had taken it in, they tested it, and said bad battery, no surpise to me. But recently, it started doing it again. I'd go to start it and got nothing; no lights, no ignition, nothing. I wiggled the wire and it started fine. The scary part is, weird things are happening when I'm driving it. The lights dim when I brake, the blinkers/windshield wipers make my headlights flicker, and the last straw was when I had my headlights and my turn signal on, and applied my brakes to stop, it flat out died while running. All lights and power steering also went out. I flipped all switches off and went to start it, but still nothing. So I do my usual (this time holding up traffic) and wiggle the wires, get in, and it starts perfectly fine.
After that happening more than I'd like, I took it in, expecting a battery or wiring problem. The professionals tested it, and came back saying it was a bad alternator, and needed to be replaced. Since alternators are pretty expensive to replace, I had to wonder: if it is the alternator, why does wiggling the connectors to the battery fix my problem. And, if it is the alternator, why do most of my problems arise while trying to start my car (I thought that was all battery)?And if it is the wiring, would that still make the professionals tests show alternator troubles? I really need help on this. Thank you for reading my lengthy description!

Answer
The problem is pretty obvious, you are losing current from the battery to the electrical system, first of all you should not even be able to wiggle the connections, they should be tight, what you need to do is replace both of the positive and the negative battery terminals with the factory OEM parts and clean the battery posts, these terminals have to be tight if you can move them there will be problems like this.