The mystery deepens in our ungrounded house

[Hassin Bin Sober]

4. You never answered if your conduit was metallic cable or rigid metallic pipe

Based on what you are saying it must be metallic of some sort. If it is metallic cable or rigid metallic cable, then that is grounded somewhere along the line. The large service drop pipe from the power lines might be grounded.

The outlet receptacles become grounded when attached to the metallic junction box.

I'm in Chicago and we don't use the third/green/ground wire because we are required by code to use rigid metallic conduit. Our conduit is grounded. Romex is not allowed.

If you want to test my theory plug your tester in to an outlet receptacle that is hanging from the box and not contacting the box. When not in contact with the junction box it will show open ground. - turn the breaker off when handling the receptacle.

The only thing that now IS'NT grounded in your home is the modification your husband made using Romex. He broke the chain of grounded conduit. If he wants to ground that device he needs to attach the green wire to the junction box he pulled the power from.