[filmo]

I once had job soldering telephone 401 cable (pairs) to telephone switchboard for weeks. Using 100 watt soldering iron. Would erode a crater in soldering iron tip after a few days. Crater made soldering easier.
Must have correct wattage soldering iron, size tip and solder for job.
After soldering 2 small wires together don't wrap multiple layers of tape over solder joint but only fold of electrical tape over soldered wire joint that is parallel to insulated wire so it is in fold with sticky sides of tape stuck together. This way minimum bulk to finished insulated solder joint.