My sons 89' toyota 4X4 has battery cable issues

The "positive" side has 2 big thick cables coming off it. 1 goes down to the starter (i'm assuming) and the other is a short one that goes into a black "fuse-box" kinda thing.

They both need replaced...I popped the cover off the fuse-box thing, hoping you could just disconnect the cable inside. It wasn't even visible from the top (looking in)

Any ideas?...or anyone have a nice setup they'd like to share?