In my bathroom, I have 1 grounded receptacle, & (1) 2 wire light switch that controls the 4 bulb light fixture. This is on a circuit with my upstairs lights & outlets, which all work with no problem. The bathroom receptacle has never worked, I replaced it after moving in house 10 years ago, & it still didn't work. Left it alone & used a screw in adapter in place of 1 of the bulbs in the light fixture. I plugged something different into the adapter, and it shorted out, no power to the lights. The breaker did not trip. Removed the fixture and checked voltage on the black & white wires, no voltage. Check V at the 2 wire light switch, no voltage. Checked V at the 3 wire receptacle, 2 volts from ground to white, zero from black to ground, same from black to white. Have check ohms , switch & receptacle are OK. Checked feeder wires in attic with sniffer, showing voltage from junction box, although sniffer also shows shows voltage in bathroom wires,except at receptacle, which showed 2 volts on meter. I cannot see any obvious problems with wires or junction box, and cannot fully trace wires all the way without opening up plaster walls. House is 50 years old, some wiring has been replaced at some point. HELP-Guesses, anything to point me some direction? Thanks

By sniffer do you mean a no contact voltage sensor?
You traced wiring to junction box in attic. Is that the same box as the light fixture box?

Despite the age, Most problems are not in the walls, but in a box/junction box. It is possible to have a problem in a box that has been covered over.
That's why code says all must be accessible.

hkstroud--No, the light fixture box is on the wall, not the same box as one in attic.

By sniffer do you mean a no contact voltage sensor?
Assuming the answer to that question would have been yes if you had answered it. Get a small multimeter. No contact voltage sensors can be misleading if you don't fully understand electrical wiring.

If I understand correctly, you have power to the junction box in the attic but no power coming out of the junction box to the light fixture box. Turn power off, remove the cover of the junction box and check all connections. Turn power on and check for voltage between hot (black) and neutral (white) at the light fixture box. Also check for for voltage at the non working outlet. Use meter. Chances are that they are both fed from the junction box and you have a bad connection there.