Electrical – How to Disconnect these Electrical Connectors

You can rent or buy a circuit tracer, true. But cheap and easy: turn breakers off one by one until the existing socket goes dead. Now work backwards, finding the nearest also dead socket. Yours likely takes off from that point.

In my experience, it's more likely that a problem is in a connection somewhere than an outright severed wire.

Start by identifying which outlets have power or not. A simple plug-in tester is an easy way to do this (as well as identify some common ways to miswire).

Next, take the covers off (but don't remove the outlets) and use a non-contact voltage meter to check if there is any power to the wires.

I'm actually hesitant to post this picture, but I couldn't find one without an idiot holding a live outlet in their hand. Don't do this. This person is one tiny mistake away from electrocuting themselves.

Hopefully what you'll find is that power eventually comes into one but isn't connected correctly, and that it continues on from there.

Check light switches and fixtures as well.

Also worth nothing: if your non-contact tester beeps, but your plugin tester doesn't show power, this is a good indication there is a problem with the neutral.

After this, if you can't identify any power in a non-working outlet, you can check working ones. You're looking specifically for a disconnect in a wire that is feeding the rest of the circuit, so logically the ones nearest the dead circuits are most likely to be doing that.

It's also possible the connections are done using pigtails, and there can still be a bad or miswired connection so it's worth checking this too:

After you've exhausted all of this, it's time to start thinking about hidden junctions and broken wires. If you know of a hidden junction, that's not only illegal but highly likely to have a problem.

You probably will have a good idea now of which wires go where, so if you can identify power on one receptacle that is likely feeding to a broken one, then you can start trying to trace the wire through the wall (and this is when you'll start opening drywall or climbing through the attic).

Your non-contact tester (especially if you have one with a sensitivity adjustment) MAY be able to trace through the wall, but it's actually quite difficult in my experience. Likewise stud detectors often have voltage detection, and this might be able to trace the wire, but again it's just not that accurate.

One thing that might also help to identify a broken wire is to check for continuity. Turn the power off, and use a multimeter in continuity (Ω) mode. Test between receptacles: neutral to neutral, ground to ground and hot to hot. If you get continuity on one or two of them, it will at least tell you that there is a partial connection and you're looking for a bad connection or broken wire. Tip: use an extension cord plugged in to one receptacle to test two that are farther apart than your multimeter leads.

Since in your case you said it was working and there were no changes that should cause it to stop, I'm not sure this will really provide you any useful information, but thought it's worth putting out there.