peugeot speedfight?

my 50cc speedfight 2 is overheating,something has melted dont know what it is but its next to the sparkplug, it has an electric wire going to it, its blue plastic and connects to something thats also melted inside a 3/4'' brass nut, need to replace these bits but dont know what they're called, also dont know where the thermostat is as this could be my prob,