Just had a proper look at this (car not used much), this is the only damage to any wiring I can see (behind the headlight switching):
Can I assume that the wiring has worn through, touched & shorted, heated up and melted the plastic insulation etc....and the only issue is to keep the brown and blue wires apart & insulated? Or is it likely to be more involved. I've no experience of car electrics, just school physics!