I have used a spiralarm type S gas detector as a decorative light above our front door. I fitted it with 12 volt bulbs in the base and upper sections. Now one of the bulbs has failed and I have to replace it. Unfortunately I cannot remember how to open up the spiralarm. I have taken off the bottom part (red light) but cannot get in to the upper part (clear glass). Can anyone tell me how to get access to the inside of the upper part? it probably screws away from the bottom but I just cannot shift it. Thank you