wiring a motion light from a switch
If you only have the red/black at the switch you won't have constant power. You also need the neutral or white wire from the outlet. Most of the time the black is the hot and the red is the switched leg. If there are white and ground in the back of the switch box take them and the black to the motion light black to black, white to white and ground to ground. If the red is hot the light won't light so you will need to swap the red and black in the switch box. A non contact voltage tester will light on the hot wire with the switch in the off position.