Soldering any crimp on connectors to car wires usually ends up with you softening/damaging the wire insulation if you overheat. Just came up with this idea while putting new radio in Harley, in past I've used small needle nose pliers clamped on wires right where insulation ends where wire goes into crimp connector (used rubber bands on handles). Don't know what made me think of this, but wet down a small strip I cut off disposable blue shop towel and wet it down and wrapped around wire. You can do it dry also then use something like a small acid brush to dip in water and wet it down. Soldered 10 wires and worked like a charm. I kept my small tin of water nearby and after soldering dipped brush and cooled terminal off. Even worked on a bear of a 10 ga wire I was butt splicing to an inline fuse holder, I re-wet once or twice during soldering, I was having to apply a lot of heat to get the solder to flow into the butt splice.