This is called a phantom voltage. Care must be taken to be sure that the voltage reading is phantom, which is caused by improper use of high impedance multimeters, and not as a result of a cable defect or improper installation, which may result in a shock hazard.

Voltage develops across the two terminal of the open circuit but electric current does not flow through the circuit because the electric current has only flowed in the closed circuit. Whenever you have a power source that is not connected to a complete circuit path, you will have a voltage without a current.

Ghost voltages can be caused when energized circuits and non energized wiring are located in close proximity to each other, such as in the same conduit or raceway. Most digital multimeters today have an input impedance that’s high enough to show this ghost voltage, giving a false impression of a live conductor.

In fact the entire area around the receptacle within 6″-8” of the receptacle might read “hot” with a voltage tester–we call this “Phantom Voltage” or “Induced Voltage.” Because it is an induced voltage, there is no actual amperage present so shocks are not an issue.

If it is jumping around with no connection or shorted connections it is most likely bad , replace the internal battery first and try it again.

If the multimeter doesn’t turn on or the display is dim you may have a weak or dead battery. If your multimeter powers up but you aren’t getting accurate measurements you may have faulty test leads. Set your multimeter to read resistance and touch the test probe leads together. It should read zero ohms.

Reason #2 a multimeter is reading the wrong voltage: Faulty Leads. If you replaced the batteries with newer ones, and you are still getting the wrong voltage readings, then the next possible issue you could have is faulty leads. Another issue could be that the probes are not connected properly to the multimeter.