The only times I see anything like that is when several loads or circuits use the same or a common ground that has ..for some reason..a high resistance..causing some back-feeding through another circuit. It is never the same voltage as the line because it is passing through another load and the ground resistance. Some of these ground "busses" or unions are within the harness and then a single lead returns to a grounding point. On some all come together at the grounding point. Need to review a wiring diagram to see what else uses the same common or ground as that system does and ohm-test their grounds only. Maybe you can narrow-down where it is. Otherwise it may be normal to have readings like that and not to worry about it.