ORIGINAL: gkamysz
What kind of 6V supply?
You will find that battery negative is the same as the braided wire on high tension lead. Check with an ohmmeter. They are system ground. The braid is there to return the spark current. The sleeved high tension wire works like a coax cable and this keeps noise inside the sleeve.
The batteries are off-the-shelf alkaline.
I did mention I did a continuity check. But my post was only a few minutes before yours. Perhaps they crossed in the ether.