Parking lights only are lit with the headlight switch pulled out to the center notch: they turn off when the switch is fully pulled out.
So I would say the obvious question is, do they work like they should, like Randy is saying, or not at all, even in the "park light" position?
They are on their own circuit and if you are not getting any power EVER at the front, power begins at the switch, then through the connection to the headlamp harness, the wiring between there and the connector to the park lights themselves, and then park lamps and sockets.
Ford began operating the park lamps with the headlamps ALSO, when? Wasn't it in 1970? Everything before then should operate only with the switch half pulled.