Without knowing exactly what that yellow/black wire it's hard to tell.
My first guess is, power or ground was not getting to that particular bulb due to maybe a bad trace in the circuit board or something. So he jumpered it with a wire to power or ground (whatever the yellow/black wire is).
Pull the wire out. Maybe the bulb won't work without the jumper wire.
But don't take my word for anything. I'm not a supporting member, have not posted enough to establish any credibility or filled out my profile correctly so apparently that makes me an idiot. So I've been told.