The most important question is what will you be powering with your new High output alternator??

If you power off another fuse panel or direct off the battery and don`t draw any power off the factory fuse panel.

You need to know your max current draw to figure what size circuit protection you need . this being the sum total of all current drawn at one time from all your new aftermarket goodies. Even though they are fused or should be except for the winch.

kinda like having a 120 amp service at home that you run two 60 amp subpanels you can only draw 60 amps total from each subpanel before the one 60 amp breaker trips from trying to run to many things on this breaker

 

Dont change the factory fuse. There is no reason to. The circuit will only pull what it needs to. Your factory electrical isn't going to pull more current just because you add a bigger alternator and wire. I think that you are thinking that if you add capacity to your alternator, doubling its output, that it puts out double the amperage. It does not!!!!!....unless it NEEDS to. Your factory circuits that draw 10 amps will STILL draw 10 amps with a higher capacity alternator. The difference is now you have an 80 amp reserve of amperage that you didn't have before for lights, stereo, etc. Your fuel injection, clock, interior light, headlights, etc. are not going to double their consumption of power by adding an alternator.

An analogy:
You make $1000 a month(80 amps-your current alt) and have a car payment of $200(current draw)
You get a raise to $2000/mo. (increase your alternator).
Your payment (amp draw WITHOUT adding anything new) does not go from $200 to $400 because you increase your available money(amps).
It only increases if you NEED it to but adding payments (new circuits i.e. lights, winch, stereo, etc)


Run a separate fuse panel, or distribution block, for your high-powered accessories and add your bigger fuse to those. In fact, I wouldnt run a fuse at all. I would much rather have a resetable circuit breaker than a fuse. That way, if you overdraw on something, you are not stuck but simply reset the breaker. A decent car audio shop will have them and all the connectors you need as well.

Something like this:


I did something similar to what you are looking to do as far as upgrading the wiring, although i didnt upgrade the alternator. You can take a look here on pages 7 and 8 and skip the irrelevant stuff. Start at post 164. I really do not think that there is any reason to install 4ga. into the fuse panel. 8 ga. is PLENTY large enough, and 4ga. is a bear to get in there cleanly, or even at all.