From what I’ve managed to figure out there’s two connections at the back, in a plastic bracket – literally the only two possible places power could go – takes Live/Neutral through a cylinder like you describe (although metal with no markings) then down to a relay (eberle 669808049) which splits off to the control board and water heater.
Machine powers on and runs with the Live/Neutral connected to them.
Question I have now is; would it matter which way around the live/neutral are connected to the terminals?