My worst mistake, was forgetting to unplug the cannister filter I was trying to get the end turned around on, because it was stuck from coraline growth, and having it come apart at the top, with water shooting everywhere, including down over the electrical wires from the skimmer and lights! NOT a fun thing to do!
My plugs were crackling, so I had to unplug everything, and clean and dry them all out, before plugging them back in!