Hy DIY.MechanicMike, it sounds like you have two different problems, the no left brake light but functioning left rear turn signal says turn signal switch problem to me. You didn't say which right turn signal lights up, front or rear, if it's the front I would suspect a ground problem with the headlights. You also did not tell us the colour of the wire you found, the colour would help us to identify the original purpose of this wire
