did that melt
in situ (on the car) or did you have some other source of heat in the area to cause that amount of damage..? looks serious..
what i'd start with is do a wire trace and find out if there are any short-circuits in the harness. a healthy
thermo switch should not have dangerous levels of current flowing through it if your circuit is healthy. you can trace the wire (which i believe is
light-green with a red stripe) to the fuse box. you will have to change the switch though.. so find a breaker. while you are at it, check that your
rad fan relay is still ok. this may be a symptom that it too suffered some damage or is the culprit..