When I turn the head lights on the left turn signal light will stay on-

On the dash or outside the truck?

If it is in the dash then check the front blink lights in the grill. The sockets will rust out and not function, Making the light come on in the dash.

It's the old style burned out bulb indicator warning system..


Turn signals dont work when the running lights are on-

Check the wiring to the taillights, the PO had mine wired wrong and the same thing happened.