This is an adjustable eddy board A16922 designed for use in ST:TNG.
1) Place the board in the location in the machine. Use a single screw to hold it in place while you test.
2) Connect the 4-pin (switch matrix) and 2-pin (sensor) connectors.
3) Turn the machine on.
4) Using a small screwdriver, turn the pot from end to end. It will rotate through about 3/4 of a turn.
5) At one end, the LED will go on. When that happens, slowly turn the pot the in the opposite direction until the LED goes off.
If the LED does not go off, your sensor or its wiring have a problem.
6) Place a ball on the top of the playfield in the sensor area. The LED should light when the ball rolls over the sensor.