I have a light box on a post that I have to feed power to but the electrical source is in the middle of the run and the switch is at other end going up steps. I was going to hook the white from light to white at power source, black from light to white from switch with a piece of black tape on it that I would hook to top of switch and black from bottom of switch to power source. Is this correct??

You're close. White from source goes to white of light. Black power lead goes to White from switch, put tape on it. Black from switch goes to black of light. Doesn't make any difference what wire goes on what terminal of switch. Any white wire carrying power gets black tape or magic marker.