Final repair of the season.

So my right headlamp bulb went out so I replaced it with a bulb of the same kind. A week later while riding I smell something burning so I look down and see that the harness on the left side is melting/smoking. So I reach down with my glove and unplug the bulb.

Should I replace the harness or did this have something to do with me replacing the opposite bulb?

Wires are 8 years old.