Yes, cars and trailers (except when plugged into a land power receptacle) have an open or floating ground. Since the only way to get a real ground is with an earth ground, such testers cannot find ground.When i got my car, an outlet tester happened to be left in it. I stashed it away and happened to find it today. I've had some trouble in the past with my laptop charging and i figured I'd test the outlet. It shows there is an open ground. My question: is that normal because the car is essentially not grounded to earth or is something wrong with my wiring?