Didn’t mean to post that pic here, but to answer your question. I always use as large a wire as I can get by with as a jumper. I have lots of scrap wire around the shop but if you don’t I would go to parts house and get a battery cable and use it for jumper. I would recommend at least 6 gauge wire. I have seen guys get by with smaller but it could be part of your problem. Smaller wire higher resistance = higher heat.