Physical effects often, but not always, reported in Close Encounters of the Second Kind, CE2.
engine failure typically occurs and is statistically more likely when the UFO is directly in front of or above the witness' vehicle, at night in isolated locations
diesel engines are immune; in cases with two farm tractors working together, one diesel and one gasoline with electrical ignition, the diesel tractor has not been affected
magnetostatic field alone has no effect; in a study for reference one below, this observation suggested the cause may be electromagnetic energy; e.g., microwave radiation
stalled engine typically restarts without assistance from the driver after the UFO leaves the area; the engine is not permanently affected
other electrical effects may occur concurrently: headlights and audio equipment may fail