I've been looking around in my engine trying to learn whats what and was wondering something. The only single cable I see coming from the alternator is black with an orange stripe... it goes to what looks like a 2 prong fusebox...then ends at the battery as a solid red wire. And it looks like an 8 gauge wire. My alternator is 130 amp and it's feeding the battery with an 8 gauge???? Seems to me that wire should be bigger. But then again I am not an electrical expert and I'm not having any electrical problems I was just curious.

The battery does have a 4 gauge wire but it snakes around underneath the truck I assume to the starter. There's also 2 negative wires and one is 4 gauge and the other is a smaller 8 gauge just like the positive wires but I can't find where those are going to.

Just trying to learn a few things is all. My truck is an 03 xl ext cab

 

Theres a lot to this so you need a lot of faith in what your told.
8 Ga. is plenty for the use.
There is a fuse in line to limit the current in any event.
The alternator may be capable of 130 amp rate but it cannot be run at that level for to long due to overheating. At crank over, the battery is normally expected to quickly take back a restoring charge that does not last very long hence the alternator and wire size is adiquite for those time intervals.
As time goes by the battery takes longer and longer to restore it's charge and is one of the reasons the alternator goes bad.
Nothing last forever and has a finite life determind by its' history of use and how it was treated.
Some people use there parking lites to excess causing the battery to be charging more than needed after restarts. Some run headlites at idle for long periods.
Some have lights plastered all over the truck that causes short life spans etc.
All these actions are wearing and life shorting uses but valid if the user thinks they need to do so.
It's uses like this that shorten the life of batteries and alternators.
Just examples.