Hi,

Over time the electrical sockets that carry heavy current (like headlights and fuses) develop little resistance from oxidation. These little resistances cause heat to the connecting part until the supporting plastic socket melts.

It helps to pull-out/push-in relays and fuses once in a while. Coat them with dielectric grease to keep the elements out.

You don't see low current terminals (AFM, crank sensor) melt as not much heat dissipated from the electrical connection.

Amarin.

p/s - also check for broken insulation to the headlight wires as these may cause over current and heat. Also check the headlight bulbs are standard (50/60W) and not some aftermarket high power bulbs to produce more brightness which needed more current to power them.