02 Ranger Edge 3.0L

The problem I'm having is the amp or battery gauge reads low when I turn the truck on. Not all the time though. I had the battery load tested at the parts store and the alt and battery checked out fine. I still went ahead and replaced the original alternator just cause a buddy of mine had a spare one, fairly new, lying around. I also had the terminals replaced. Battery is only 2 years old.

And when it does read low, wiggling the battery and alt wires around shoots the gauge up to where it's supposed to be.

So here's what leads me to believe the battery cables are at fault here. The cables that connect to the positive post are stretched and frayed, so cutting them back even an inch won't have a good secure connection. And the negative cables have some corrosion and are also frayed. Replacing the cables is probably the best option, but I don't know how to begin.

​​​​​​Do they just simply unbolt from somewhere or do I buy a whole harness? From the looks of it, they crimp into a terminal thats bolted by the fuse box, right?