Turn signal gremlins

[BigAl47]

Have a 72 f250 360 auto 2 wd
My problem is left rear turn signal. Everything works headlights,running lights, turn signals,
Emergency flashers etc. until I turn on the headlights then the left rear turn signal doesn’t blink.
Also the dash blinker doesn’t work. But when I turn the light off it starts to work.
Thanks in advance.

[cep62]

Make sure you have a good ground.

make a temporary long ground wire to the battery neg.
If it works make a good permanent ground to the body / frame.

[BigAl47]

Got everything working. It was the ground. Cleaned all contact areas and just like magic things all started working

[cep62]

electricity is like water , it takes the path of least resistance.