I own a 1964 Impala. When I put on the left blinker, the headlights come on and flash the same as the blinkers. When I put on the headlights, the left blinker on the dash stays on. I have tried to clean up all of the grounds that I could find. It only seems to be affecting the left (drivers) side of the car? Can anyone help?

you most likely have a wire in the harness shorted out most common areas for that type of problem is in the trunk, steering column, firewall pass through or engine compartment

Thank you! I will check it out.