High amp alternator help

[MaximRecoil]

and replace the fusible link with something a little more reliable.

Why do you say that fusible links have reliability issues? They are not supposed to work exactly like a fuse, i.e., they can handle brief spikes without blowing like a fuse would. They are intended as last-ditch protection for the wire against a hard short-circuit (such as the type that can happen in a car accident when body steel pinches through a wire), and they are perfectly reliable for that. They are normally used on e.g. the alternator-to-battery charging wire, which can experience a lot of spikes that don't cause harm, but could blow a fuse. Additionally, fusible links can be more reliable than fuses in a different respect, i.e., long-term connection integrity, because they are hardwired inline, while fuses are usually press-fit into a socket. That aspect can be more or less negated though with certain types of fuses/holders. Personally, if I were replacing a factory fusible link with a fuse, I'd use an ANL fuse, because the terminals on them are designed to be bolted down. 

[Pete in NH]

As you say fusible links are kind of last ditch protection devices. One of their issues is that it is hard to know exactly when they will melt and open other than catastrophic overload. Wire gauge size and length of the fusible link come into play on when it will melt. All in all they are rather crude devices that auto makers eventually moved away from in favor of heavy duty slow-blow type fuses.  One of the issues with fusible links is getting a proper replacement if they do open up. Here the length factor comes in and it's important to match the original section of fusible link in gauge type and length. I think in the end, field replacement issues were a major factor in going to real fuses. If you look at the heavy blade type fuses used to replace fusible links the fuse blades are wide and thick enough to handle the current. Yes, a solid bolt in type would be better but at a much greater cost. There are many types of fuses and characteristics on how fast they will respond. These big automotive types are a slow-blow type of fuse which means they will not open on transients but require a defined percentage of overload for a specified period of time. As an example 200% overload for 30 seconds. This may or may not be the real characteristic I'm just using it as an example. An engineer can look at the published specs. for the fuse type he wants to use and know how the fuse will react under certain conditions. The fusible link being a piece of wire can have many more variables that are not defined as to melting point not to mention if a field repair was  done properly.

[MaximRecoil]

Here the length factor comes in and it's important to match the original section of fusible link in gauge type and length.

Three inches long and four AWG sizes smaller than the wire it is to protect is the standard, e.g., 12 AWG fusible link to protect an 8 AWG wire. They are definitely more of a pain to replace than a fuse, but if you have a step-down butt connector, a ring terminal, heat shrink tubing or self-amalgamating tape, and a proper crimping tool, it isn't too bad.

Informative post, by the way.