New inverter pump installed, not working, what could be wrong?

I have also experienced issues with a low 12V. I also like to do very simple things to start out with when I have a problem - like check the basic electronics such as grounds and reference voltages. Designers and programmers of these systems are very diligent and smart, but they are not omniscient. If I was a slave to the codes (whether present or ABSENT), as if they were infallible, I'd have caused myself a lot more trouble over the years than I have.