I had the starter end of a 12V cable wear out and corrode on my Jeep. The cranking got slower and then intermittant. I found it when I saw it glowing one night after I started the Jeep. That was dangerous so I replaced the cable.
Too-small cables will get warm and slow down cranking speed fairly significantly. I like to use at least #2 cables for 12V and 2/0 or 4/0 cables for 6 volt, especially when the battery is mounted in the floor or trunk.
I am running 2/0 cables on my truck with 12V because I converted from 6 after I changed the cables, and the cranking speed is great. Of course, I am running a 6V starter, too, but the lights hardly dim when I am cranking.
