Cant figure it out, shes always been so good.

[Smallz72project]

So this is driving me nuts and I'm hoping someone might have a word of wisdom to point me in the right direction. It all happened a few weeks ago, I got in old blue (72 GMC) and started up fine like she always does, drove her over to my sisters house and when I left there to go to the gas station once again she was fine. Go to the gas station run in and when I came out, turn it to the on pos. and the radio came on and then when I went to crank it over it clicked and then absoulutely NOTHING!! popped the hood and wiggled the positive cable went back and same thing. So I figured it might just be a lil loose so I tightened it up and still nothing. So disconnect it (side post mount) and find out that the cable end has corroded completely through. So while I am tinkering with it for like 20 minutes and about 30 people just walking by gawking without asking if I needed help, I get ahold of my brother in law and have him bring me down another cable end. Get the end on and it starts up like a champ on the first crank. Get her home and the next morning ABSOLUTELY NOTHING again, check the batt. voltage and its fine, check the voltage goin to the starter and thats fine, I've looked at it and cant figure it out for the life of me whats going on. It is a wiring nightmare but I just dont know why one minute fine then the next not. Anyone have a similar problem or advice? It doesnt turn over or even click, but all the accessories work. Any help is greatly appreciated and much needed. Thanks in advance guys.
Todd