Here is what the head service tech had to say:
I had run into this before, the customer ended up just powering the T7C on and the issue went away..... However I'm not sure if that is possibly damaging to the T14SG/vice versa.
I do think in this instance usually you will see the T12FG trainer cord being used but we do not have a lot of documentation on it so I'm not sure if it steps up the voltage or steps down.
Or if the 12FG cable allows for the signal and power to be transferred and not the power.
Not sure that helps, but it is a start. Too many combinations for anyone to have experience with all of them.