Driver side turn signal not working

Welcome to 2CarPros.

Based on the model year, the first thing that comes to mind is a weak ground. The ground for the left brake light and signal are the same. Take a look at the picture I attached. It shows the wiring and ground (which I circled). The ground is on the frame of the vehicle. It will be bolted on. What I suggest is to first check the ground to make sure it is clean and tight, free of corrosion. Also, when the signal isn't working, move it around to see if it makes it work.

If you are confident that the ground is good, then check the light socket itself. Check for the same things, corrosion, pushed in pins, loose connections, damaged connectors and so on. Also, when the light isn't working (brake or signal) check the socket to see if there is power to it. Use a test light and connect it to a known good ground.

Here are a few links that may help:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-check-wiring

If you could, describe what happens when the signal doesn't work. Does the indicator light up inside the vehicle and not flash? Does it flash quickly?

I have to be honest, I suspect it is related to a bad ground, but the only way to be sure is to check. The ground may be weak enough that when the lights are on, you lose the signal and brake lights.

Please let me know what you find or if I can help.

Take care,
Joe