The two important test points are Ref to ground and the base of Q2 to ground. Ref to ground should vary with Rtot and, of course, the approximate battery voltage at the time of measurement.

Another point is the Base to Emitter drop and the Collector to Emitter drop of Q2.

So, see what you get,

 

KISS,
When you refer to Q2, I assume you are talking about the TL431. I'm a little confused, almost certainly from my ignorance.
The data I have on that transistor refers to the terminals as K (cathode), A (anode), and R (reference).
Using that terminology, with the power source being 12.7 volts, the readings I get are:
A to ground = zero
With Rtot at one extreme:

K to A =7.4 v
K to R = 154 mv
R to A = .89 v

With Rtot at the other extreme:

K to A = 150 mv
K to R = .4 mv
R to A =.1 mv
Naturally, I have no idea what this means.
Thanks for the help.
Don