I really like the XT60/XT90's...I have a fat-tip 100W soldering iron. I agree on the mating of the male and female before
soldering. Once I held an un-mated connector to the soldering iron too long, and the pin sagged (no longer aligned straight) when the plastic got too hot and soft. I also take needle-nose pliers and rotate the pins so the solder cups face the side when the conector is laying flat.
Slide a section of heat-shrink onto the wire, strip the end insulation to a length about 3 times the copper diameter. Twist the ends of the strands to smooth them out. Set the hot iron so that the tip is suspended, and hold the wire tip up to it while feeding solder into it with the other hand. "Tinning" the wire tip just takes two seconds. Don't apply a blob of solder, use only enough to turn the wires silver.
Next, take the two mated male/female connectors and drop a short cut-off piece of solder and set it in the cup. Hold that cup up to the iron tip until the solder chunk just melts, and at that moment, insert the tinned tip of the wire into the solder cup that's on the shank of the pin.
This can all happen pretty fast. Pull the assembled connector(s) and the now-soldered wire away from the iron, and blow on it to cool it. Slide the heat-shrink over the joint and heat it up to seal.
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