What exactly is a "Fusible Link"? and how would I fix one? This might be what is wrong with my car. Thanks

 

It's basically a small section of wire that is a smaller gauge than the rest of the wire. It's usually wrapped in a thick rubber-looking sleeve that's designed to bubble when the link melts, indicating the link has bitten the dust. You can see one right next to the battery if you want to know what it looks like. You fix it by cutting it out and replacing it with a short length of wire the same gauge as the original link, then wrapping it up, or some parts stores sell "pre-made" links (though I haven't seen one in a while, not that I've been looking).