Looking to do some tack welding on a cheapy Bestop box, so that I can take it to someone to weld up properly. It's 16 guage steel. I linked up the batteries like this article.... http://www.safari4x4.com.au/80scool/tech/batweld/batweld.html and the middle battery positive post just about cooked off when I first began to do the first weld. what did I do wrong? any advice?