Try cutting the wire at the back of both sensors (leave yourself about a foot of wire or so) Take them to the back of the motor head and hook both the white wires from the sensors to the white terminal on opener. Take the white wires with the black tracer and hook them up to the black terminal. You should have one sensor that lights up automatically and the other sensor will light up with them aligned.

If they work fine at the back of the unit, then you have bad wires and need to run new wiring. If only one is lighting up and not the other, you have a bad set of sensors. If neither one of them is lighting up, you most likely have a bad set of sensor but could possibly have a bad circuit board.