Hi Michael,

First, yes you can connect the tuning aid between your transmitter and
feedline.  It should give you indication when you use the auto tuner in your
radio.

Typically, these tuning aids are connected between the final rf output
source and the input of the tuner.  By this I mean your rig or amplifier,
whichever is the final source of output.  Thus you can use your tuning aid
to tune up your amp.

On the settings on the tuner, they often have presets listed in the manual
and you could try these.  Otherwise, you will need to experiment a bit.  One
fairly good method is to adjust your tuner for maximum receiver noise and
this will often be close to resonance.  You might also invest in one of
those tuner tuners from Palomar, I hear they work well.  One thing I have
done with my Tentec tuner is to make myself a cheat sheet of settings for
each band and antenna.  I find I can go back to those and be very close each
time give or take current weather, rain, etc.

One final question on your tuning aid.  I don't know which type you are
using but most of them I've used that are strictly RF sensing devices rise
in pitch with power output.  You mentioned yours decreasing in pitch.  If
that is truly the case then go for it but make sure that is what it is
supposed to do before you start tuning an amplifier.

Good luck, I hope all goes well and very 73.

Kevin :)
Amateur Radio:  K7RX
Navy Marine Corps MARS:  NNN0SHS