Hi Group, probably old hat, but even a one-liner response would help.

The brother-in-law has a holiday home. Mains electricity - but at a
distance.
I am an electrical engineer (retired - the theory type - not so experienced
on the practice).
He asked me to help with sorting the wiring for the lighting in the house.
A long corridor with dual switches for overhead lights. Been there for many
years.
Not sure if it was ever right - he did some amatuer DIY on it and maybe
changed things . . . screwed it up. . .
Some lights come on when switch A is on, others when switch B is on . . .
A mess.
So, I pulled back the wall switches and did some simple probing with a neon
tester.
Some wires showed a bright neon - obviously live.
Some showed no light - not live.

BUT SOME WIRES SHOWED A DULL NEON LIGHT - when other switches were turned on
these became bright.

I has assumed it would be easy - which wires were live - light or no light -
draw the diagrams etc etc etc.

So, my question please. If a neon tester just glows a bit, can this be due
to seeing a neutral with a long run back
to the local supply trafo and hence with some small voltage drop?
Can a neon tester (the screwdriver handle type) register a few volts on the
neutral?

Or am I losing it totally? Missing some point?

Any advice (be gentle, please) appreciated.

Ger

P.S. Plan B is to switch off the supply to the house, isolate all the wires
from the switches and use a meter to trace the wiring.