Given my mom's car, I measured a voltage in an electric connector equal to the voltage across the car's battery. This is when the multimeter is connected to the connector supply pins. If I take the negative terminal and put it on the car body the reading is now 0. Somebody told me on the phone why this is happening, I didn't understand very clearly so I came here to ask for help. Can someone please explain to me why is this happening? Why is the multimeter giving me that voltage measurement even though it doesn't truly exist?
Thank you in advance and sorry if the answer is obvious.