George, it's only for testing the TIU, not for permanent connection. The one downside of this design approach is due to the parts used (cheap was a primary goal), you have to calibrate each unit using the pot on the board. That being the case, I'll probably just calibrate mine using my 'scope for around 11 volts P-T-P for the "good" signal. The "bad" signal ends up being approx. 50% of the amplitude of the "good" signal, in this case around 5.5 volts P-T-P. If you have a known good TIU, you can simply use the good channel as a standard and calibrate so that the good channel indicates a good signal. In my mind the "bad" signal is primarily to tell you that the TIU is putting out some signal, but appears to have a weak channel. I envision the unit to be calibrated to really require the "good" signal to consider the TIU channel to be fully functional.
The usage is to simply power up the TIU, and connect voltage to the input of the channel being tested, and the tester to the output of the channel. Power up the tester and check the lights, job done.
I'll be generating a BOM for the parts in the near future, so many projects, so little time. 
