Up in the attic. Have to bring hot wire to junction box with three
legs going out. Each leg goes to ceiling light of different rooms.
YES, I can power them up and the wall switch in each room turns on
its respective light. BUT, what's an easy way to test that I don't
have hot and neutral reversed. The old romex in the attic (two wire,
cloth wrapped) is NOT color coded in any way.

Do I simply drag a neutral wire from a different circuit and probe
the bulb socket in each room? Is there an easier way? My A.C.
voltmeter obviously does not indicate polarity.

All replies appreciated. Sheetrock guy is coming tomorrow a.m. and I
have to solve this today!

Ivan Vegvary

It's not an actual polarity you want; remember, this is ac. The
"polarity" applies to which is hot and which is neutra.

Arbitrarily assign one as Hot (H); use the wire to the hot connection on
the fixture as H:
Find an Earth Ground (receptacles are probably earthed).
Then, check
H - N 120V
H - Earth 120V
N - Earth 0V

If H - N = 0 then N - Earth should be 120V, meaning they are reversed.
Switch the wires with each other.

Assumption: Neutral and Earth are ONLY joined back at the breaker box
and nowhere else!
Validate Earth connection by turning off all power (Mains). Use your
ohmmeter to measure the resistance between Neutral and Earth. It should
only be a few ohms, depending on the length of wire involved, or maybe
0.0.
SWITCH YOUR METER OFF OHMS AS SOON AS DONE, so you don't accidentally
try to measure voltage with it.
The reason to turn off all power is that, should the polarity be
wrong, you will fry your ohmmeter. I always check first for voltage and
only after knowing it's not 120 V ac do I switch it to ohms. Then as
soon as I finish ohmming thngs out, I put it back to measure ac voltage.

HTH

Twayne