When I turn headlights on my tail lights work but when I hit the brakes my left

Repair the ground circuit to that bulb... Likely need a new *bulb socket*... To test, you can use a piece of wire with insulation stripped back about 1/2 inch on each end... touch the bulbs brass base with one and then touch a metal ground with other to see if light now works as it should... You can turn on lights and left signal for testing, or have helper push brake pedal... **GROUND THE BULB!!**