Welcome to 2CarPros.
I have to be honest, that doesn't make sense. The two aren't connected. Can you tell me if the right rear light works with the hazard lights?
I attached two pictures. The first one shows where power is coming from for the right brake and signal lights. The power supply is for both left and right, but they break out separately.
Picture 2 shows the tail light and note the same color wire going to it. That comes direct from where pic 1 shows.
Now, since the parking light works, it most likely isn't a ground issue. We know the fuses are good or the left side wouldn't work. So that leaves me thinking something happened to that gray/light blue wire. With that, I need him to check that wire to see if it has power when the brakes are applied as well as the signal.
I am very interested in knowing if the hazard work, because that would then eliminate a wire issue because it is the same one.
When you check the rear light, there will be 3 wires. If you look at the pics I attached, you will see that one will have power when the parking lights are on, one will get power when the brakes or signals are on, and one is a ground. We need to check if power is present.
Here are a few links that you may find helpful:
Let me know if you have questions or need help. Honestly, I looked through the headlamp schematics and don't see what he could have done to cause this.
Images (Click to enlarge)
Thursday, August 1st, 2019 AT 9:16 PM