[Paul Dorman]

I just repaired one of these, and I notice
there isn't a way to visibly see if the box
is feeding the guitar's (or any other instrument's)
signal into the internal speaker, or to the output.

This is important to know, because if you look at some
of the Talk Box hook-up diagrams online, you will see some
configurations have nothing hooked up to the output,
which is risky, because you could initially have the
amp feeding the Talk Box, in a no-load condition, which
could damage the final amplifier stage.

I understand why they don't have any visual indicator,
because talk boxes are totally passive devices, but it
makes it a bit dangerous to use, as you cannot use a
multi-meter to measure the 8 Ohm speaker impedance on
the input cable, due to the DC blocking 15uF capacitor,
which rolls off the low frequencies.

So it's safest to always put a proper speaker load on the
output, and it looks like most people use them like
this anyways, so it's probably not a big issue.