I just moved to a house which was built in 1958 (almost 60 years ago).
One GFCI outlet has the indicator light on but no power when plug in appliance. So I opened it and measured the voltage with a multimeter. It is very strange. See below diagram:
I guess A and B is input line whilst C and D is output line to other outlets. When I measure it, I have removed the GFCI receptacle. Why A and D still has 5.5v?
And I didn't find ground line from the outlet.
If I connect A,B to LOAD and C,D to LINE of the GFCI receptacle my receptacle indicator light is on but recepacle itself is always off. When I press the reset/test button there is no effect.
I still cannot figure out what's wrong.