The connection between the stator and R/R has to be secure and tight as far as the connector pins, the wire crimping of the terminals and pins, etc. If there is a poor or loose connection, improper wire and terminal gauge size, you will get increase in resistance which results in heat and melting. In terms of soldering instead of using a connector, you have to know how to intertwine the wire strands to get a proper solder connection involving all of the strands of the cable. Otherwise a cold joint will occur and once again, increase in resistance. The same goes for knowing how to do a proper crimp. Did the new R/R come with a factory connector to mate up with the stator half? Sometimes the factory uses wire gauge and connectors that aren't the best to save money in production.