on the matter of contact resistance, a circuit with a 1 ohm d.c. load
draws about 14 amps (like a fan), and then even a 0.1 ohm contact
resistance hardly effects overall current draw. therefore, heat is
generated at the rate of .1 x 14^2 = 20 W at the contact resistance,
presumeably over a small area/volume, which would wasily account for
observed damage.