How do I turn the headlights completely off while the car is on?
There should be a knob or a switch that says auto, then a symbol of 2 headlights facing outwards and another symbol. Youll turn that knob all the way to the left.
If you arent sure what the knob looks like, just go to google and type in your car make/model and year and then add headlights switch, should be a few images for you.
If you mean the daytime running lights you will have to find a dealer that is willing to turn them off with a scan tool. in most states it is required by law to have them on newer vehicles.