Yup--they work all the time,with or without the key on,or engine running. I had a stoplight switch go out of adjustment on one of my trucks,the clip thing let it slip out of posistion--the next morning the tailights were still on,looked like candles--and the lenses had melted spots in them /forums/images/graemlins/eek.gifand the battery was dead enough to have to jump start it--good way to start the day in a good mood,aye??. /forums/images/graemlins/shocked.gif