Well, I saw something.
When I am looking at the sensors, as I am "directly" looking at them by pin number, I realised I am using the "wrong" pins.
LED 5 is looking at Pin 13. That's the onboard LED.
That isn't going to work.
Ok, so That is one problem detected. I shall have to change the assigned pins to the analogue inputs.
Though that is going to be a problem as I need 6 inputs and two of the 6 analogue inputs are the I2C bus on which the RTC is going to live.
Hmmmmm... But anyway.
That aside, I see I can't use the pins listed in the sketch. BUT - and isn't there always one of them? - even if I negate the reading of the sensor pins for LED 5, it still doesn't glow.