I was working on the alternator of my friend's Camaro the other day, and the wire fell apart in my hand. I wasn't planning on working on cars that day, and I was away from my own tools. He needed a new wire with connection lugs ASAP. I like to solder connections like these for the superior corrosion resistance and lower series resistance soldering has over crimping. (Crimping is a half-ass way out.) With only a bullshit pen iron, I made it happen.
We know from "common sense" that if you're cold, a blanket will warm you up. Nerds call this Newton's Law of Heating and Cooling. *1
Since heat energy can't be created or destroyed, heat in equals heat out. The heat we generate is the same as the heat we lose. The bullshit iron is only going to generate so much heat, so we need to figure out how to keep it. We need a blanket.
I used aluminum foil to keep the fresh air away from my wire. I put a dollop of solder on the wire (to help heat transfer from the iron) and heated the wire hot enough to sweat its own solder. It worked very well. Keeping the flux fumes nearby probably helped me avoid corrosion of the copper, too. I used a rag to insulate the wire away from the work area since copper is a fantastic conductor.
*1 Both convection and conduction are at play here, but convection is probably easier to grasp. To be rigorous, you should consider the series resistance of convection to the blanket and conduction through the blanket. To be impractically rigorous or to show off your new FEM toy, you would consider the air trapped by the blanket.