"...flicking the all-important switch from SCE to AUX."
Not quite. Not "from". The instruction was: "Flight, try SCE to Aux."
i.e. Set the Signal Conditioning Electronics (SCE) power supply from normal power (NORM) to use Auxilary Power (AUX) instead.
So it's not "from" SCE to Aux. It's just: SCE to Aux.
But still, full points for including the Apollo 12 reference.
Ref: http://tryscetoaux.com/ for complete details.