Woodenfish
Member
Plastic melts at a lower temperature than solder so what you witnessed is normal. When I use this type of connection I first strip the wires the proper length so when the wire is inserted it just clears the solder ring. Never twist the two wires before inserting them in his way the stranded wire can intermingle and you get a better connection. Also, continue to hold your the newly soldered wires until the whole thing cools down. If you aren’t careful about that you could get some really interesting shapes in the shrink wrap.