Possessed 2000 Electrical system

Trucks been running fine, went out this morning and turned the key. Everything started flashing and going on and off (including the stereo, and all idiot lights) like someone was connecting/disconnecting the battery. Eventually it stopped, but then something would beep every once in a while, and everything else was completely dead. Pulled neg. battery cable and it looks fine. Pulled the positive and wholly crap, there's only about half the bolt left, with only about 2 threads left on the very end! Battery tests fine. Any suggestions on what might be causing it to eat the cable bolt? The terminal on the battery is sort of dark/wet on the inside, not sure with what, since I had to quit messing with it and get to work. Hopefully replacing the cable will take care of it, assuming that is the actual problem. Just curious what might have caused it in the first place?

sounds like battery acid. make sure your battery is not leaking. it could have been from another battery that was replaced. check your battery for leaks and bulging of the case. if it is replaced it. you are definetly going to need a new battery cable. go the the auto parts store and purchase some battery terminal cleaner. it wil nuetralize the batter acid and prevent anymore damage. make sure you spray it on the battery tray as well.
good luck.