You could try it by leaving the points cover on and connecting the earth wire of the bulb to the kill button terminal but remember that the magneto low tension coil is always connected to the points and that coil has quite a low resistance so there might not be much difference in bulb brightness between points open and points closed. You would do better with a cheap multimeter set at the lowest ohms range. With the meter leads going to the kill button terminal and earth you should see a change in resistance when the points open and close.
