Today I went to replace an old non-GFCI in my bathroom with a GFCI outlet. After completing all the connection, the outlet tripped immediately as soon as it was reset. I disconnected the load side, and the outlet operated normally. I did some continuity tests and found that the line and the load neutrals showed continuity when probed. I assume this is because neutral and ground have continuity somewhere on the load side, which obviously has to be fixed.
I then went downstream of the GFCI to the switch for the vanity lights (which shares a box with another light switch), and found that in addition to the other light switch, there was an additional daisy chain that appears to feed all other outlets and fixtures in the bedroom and adjacent hallway. When I disconnect those wires from the line and cap them off, the GFCI operates as normal, as do the two lights connected to the switches.
So I’ve narrowed it down very slightly, but it seems daunting to try to find the fault from this point forward. I assume I need to leave the chain of outlets disconnected from the line, then check for continuity from neutral to ground at each outlet and fixture until I find the one where it exists. Is this correct? If I knew the order of the connections, I could do a split-half search but since I don’t, I guess I’m just looking at each outlet (and potentially each light fixture or switch) one by one until I find the fault?