ASE wrote:
Ceiling light fixture was blinking in and out. Replaced the switch
(single pole, no outlet or anything else in box). Now nothing at all.
Old house, mostly old wiring (knob & tube). $2.00 little voltage
tester, the kind with two prongs and little christmas tree bulb, shows
no juice at switch (touch ends to the exposed wire ends) or at the
fixture (again, touch ends of tester to exposed house wire in box).
Have checked and turned off and on circuit breaker (upgraded panel),
and no problems with anything else on that circuit. Do I need to try
a better tester, or is everything fried somewhere in the line, leaving
the choice of no more fixture or ripping apart plaster in old
house(cha-ching cough cough)?

There are many possible issues. I am going to suggest that from the
information you have provided, you are not really ready to go about checking
for this kind of problem.

Are you familiar with the various ways a light and switch may be wired?
Have you tested the wires in a way that would account for all those ways?

I suggest that you may want to start by buying a good book at the DIY
store or book store and read the section on home wiring. Learn it will
before you start working on this project. Old homes can have many surprises
in the wring. Someone who does not really understand what is going on may
see something that may look OK but it may be a dangerous situation unknown
to them.

You may want to call in a professional.

I am sorry, but from the information you have provided I can't offer
specific advice on how to proceed safely in this kind of forum.

--
Joseph Meehan

26 + 6 = 1 It's Irish Math