In troubleshooting one circuit, I accidentally discovered information for a second circuit that I've also been trying to sort out. So, bottom line is I was stupid and lucky. While replacing a switch on the first circuit (breaker off), I accidentally touched the hot to ground on a switch next to it which is on the second circuit (breaker on) with a ground wire and the lights on this second circuit came on.
This second circuit is a combination of lights and outlets with branch circuits. Part of this circuit works and part doesn't. As I said above, when I jumpered hot to ground, everything worked. I think this means there is an open neutral somewhere because the circuit was completed when connecting hot to ground. Is this correct? If so, how do I find the open neutral?