b51r,
What is the part number of the 6v ground cable you got from JC?
What is the part number of the other/positive 6v cable that you got from JC?
My experience has been that it is common for vendors to sell a 4 gauge (12v) braided ground cable for a 6v system. 2 gauge or bigger is better (I like 00 gauge). The ground cable does not have to be braided - Tractor Supply should have large-gauge non-braided cables.
Just in case the "8v battery solution" is soon suggested, check the cables, first.
