Working on a practical lighting effect for the gum machine in Charlie and Chocolate Factory I had two different colored floodlamps in some old household flood fixtures, hooked up to a chase controller. I was having trouble with the chaser and one of the floodlights, something similar to one of these: The lamp was wiggling around, so I turned off the chaser and took out the lamp. There was a loose screw, and I proceeded to tighten it. I touched the hood and ZAP! Owwww! The stupid chase controller was screwed up and didn't work right at all! It was sending juice even though it was off! Lesson learned: take precautions.