Had fun working on this one.
Probed and probed with the meter.
Then read the wiring diagram for the lights.
Did you know that the front marker lights are wire in series ,power in to marker lights then out to the front marker/running light then to ground.
That said, if the ground on the front dual element light is bad,..it will back feed through the power side of the dual element bulb, up the power side of the turning light and do all kind of wierd stuff.
We replaced the front left dual light socket and all was fixed.
I love trouble shooting electrical issues!
I miss doing that...did it for 20+ years now I embroidery and screenprint?...
Let me know if you'll need anything else.