I assume the bottom threaded line with the thermoswitch or flow switch is the cold water inlet.
No, the threaded coupling on the right is the cold inlet. The left-hand one is the outlet to which the shower hose attaches; the device with the blue wires is the protective thermostat. There's another 'stat mounted on top of the heating canister which acts as a main thermal cutout.
The other tube running from the bottom of the canister is just a pressure-relief outlet should there be both a blockage and a main cutout failure.
http://www.shower-spares.co.uk/triton/tx7000i_and_tx7500i.htm
