Why would a wall outlet read 12 V AC at 3 kHz?

Question

I have an exposed wire coming out of a wall, I believe the old owners of the house had a wine fridge or some other appliance installed in the space. I went to install an outlet on this wire and measured the voltage with a Klein Tools MM400 multimeter. When I measured the AC voltage, I measure about 12 V at 3 kHz.

Of course, thinking I wasn't measuring it correctly, I measured some other outlets with the same settings, and every single outlet measures 120 V at 60 Hz, exactly as you would expect.

What could possibly cause this reading?

The house has a solar PV system, but nothing from that system wires into this side of the house. The PV inverter is on its own breaker, so I don't see how this could be from the PV system (maybe I'm wrong).

The house also has an electric car charger that is wired into the circuit breaker cabinet in the garage, but it also has its own circuit, so I don't see how that unit could create any interference either.

I'm at a loss on this and would appreciate any insight on this. I'm requesting an appointment with an electrician, but I'd like to here what stackexchange thinks about it.

UPDATE Based on some other posts I was reading, I did some more investigation.

1. The above reading was line-to-neutral, I measured the current and I get 365 mA. Now that it is morning and the sun is out, I'm measuring 12 V at about 10 kHz. I suspect that this is capacitively coupled noise from my PV inverter as this equipment uses a PWM driver for regulation, and they tend to operate at low kHz frequencies.

2. When I measure line to ground, I measure 120 V at 60 Hz with 2.5 A current. Measuring neutral-to-ground gives 0 V.

UPDATE 2

While turning off breakers to start searching for a loose connection, I found that my problem wire is connected to a dedicated breaker, there is nothing else connected to the circuit. Apparently I was mistaken about where the line starts.

Since this is the case, I'm assuming my open neutral connection is exactly at the breaker. I suppose it's unsafe to just cap the neutral line and bridge the ground copper to the neutral screw and the ground screw on the new outlet...

For reference: Electrical: Can a neutral wire just be capped?

Answer 1

Bad Neutral

Figure out what else is on the circuit. There is likely a loose, or bad backstab, neutral connection.

Definitely not safe to connect anything until you get a good hot/neutral reading. Do not bootleg neutral to ground - it will work but cause very unsafe conditions in the rest of the house.

According to comments, this is fed by LOAD of a GFCI/receptacle. If checking/reconnecting those wires does not solve the problem, pigtail the wires to LINE instead of LOAD. If that works then you have a GFCI issue. If that does not work then you have a bad wire (e.g., nail through a wire in between the two ends).