Unknown circuit - 43 Post, possibly others

Does anyone know what the 120VAC breaker labeled "Ext Outlets" goes to? I'm not aware of any external to the house 120VAC outlets except the one on the bridge, which is on the "Quartz Lights" breaker?

The back story to asking:

We have been to numerous marinas with the new spec power pedistals and had no problem until last weekend. We had been at that marina a couple years ago also with no problem. We were able to get a workaround so we could stay. Back at home I went to check the ground to neutral's (I had fixed a problem from PO wiring several years ago). I easily found a new short (fluxuated a lot but as low as 2 ohm and high as 100) between the "A" neutral bus and ground.

I disconnected neutrals one at a time and tested until the partial short went away. The neutrals are grouped 2-4 to a lug. I left the suspect lug disconnected and connected to shore. Every breaker I turned on and checked, everything worked. The only breakers I can't easily check to see still works are the block heaters (I know which neutral they are on as that is what I fixed several years ago) and the "EXT OUTLETS".

I expect the EXT OUTLETS is wired but not used so there are dead-head lines somewhere in the boat and over the years one has had the insulation protection fail so there is now a partial short, likely being wet. Problem is I don't know what 'could' be connected to them so don't even know where in the boat to look.

Thanks

Only wires under the cockpit comings are for the 12 VDC cockpit lights, unless they don't exit the plastic tube and stay in engine room.

Quartz lights are on the hardtop (aft facing), and a 120VAC outlet box inside the helm console that now runs the Starlink. Engine room lights on ours are on the 12VDC sircuits.

Thanks. There was one in our engine room. Installed by a PO using romex and hooked to the ice maker circuit. I removed it LOL.

Mine has the phone inlet alongside the power inlet. It used to have two shore power inlets, they were removed and the current 120/240 50A inlet put in it's place. The external shore power goes to two separate (A & B) breakers on the corner post in the interior directly above the outside recepticle. Power runs to two (A & B) dual breakers in the main distribution panel on the back galley wall.

The ground/neutral problem is past the breakers in the distribution panel, as when the A breaker, load and neutral, is open there was no trip. Also the B breaker and all it's sub circuits worked fine.

Getting a quote for an isolation transformer, but for now just leaving the unknowa neutral bundle disconnected.

There are no 120 volt in the cockpit or main deck.
There is one 120v on the bridge, which is on a "B" circuit and works (runs Starlink).
There are two 120v in the engine room, on a known breaker, and work (battery chargers).

I haven't yet found any 120v, lights, appliances, outlets, I've used that isn't working with the suspect neutral(s) removed.

I've never had or used a circuit tracer. How far away can they detect, since all the wiring is behind panels, floors, ceilings? Can they be used on a deadended circuit?

I went back into the panel and the EXT RECPT breaker doesn't have an ouput wire so has never been active on our boat. Finding where the bad neutral goes is an academic issue for now. I will look into the line tracer for another time when I'm up for crawling through the internal spaces following wires. I've been changing my 65 Corvette to a new fuel injection system, removing all the old wiring and installing new ones, and for now my somewhat older body has had enough bend, fold and spindle.

Thanks

There are a few things you can check yourself if you have a digital resistance meter.

Turn off all the 120v main breakers on the panel and remove the shore power cord.

First check the shore power cord to see if there is a circuit between any of the 'pin' circuts and the ground plate on the side (I'm presuming you have a 120/250 cable) If there is the cable is bad.

Next go to the panel and turn off all the individual 120v breakers, and the A and B 120v master breakers
Open the panel and check for a circuit between the A neutral bus and the ground bus, then the B neutral bus and ground
If there is (like I had this last pass) you can disconnect the individual neutral lines on the bus that had the circuit one at a time until you find the one that has a circuit to the ground bus. Then insulate it, reconnect shore power, and test circuits on that bus one at a time to find which one no longer works.

If there is no circuit from either bus to ground with all the breakers off, turn on breakers one at a time starting with the bus master and re-test. When you find a circuit between the bus and the ground someting on the circuit just turned on has the problem. (In my earlier case it was the block heater circuit. I opened and checked all the points on that circuit I could access. I found one junction box where the ground and neutral had been crossed.)

If everything works, then you may have the same unknown issue I have. But if everything works you can go boating.

-g