John,according to the installation instructions, the switch is connected to the heater by a multi-core cable, which is shown with moulded plugs at each end. Being a `sealed` cable it gives no info as to the colour of the wires within. It may be possible to get a new cable or one from a breakers.
At the switch end,it states that there are fuses on both negative and positive inputs, and confirms theDIN wiring code as blue=12V d.c positve (live) and white=12V negative (earth)
I don`t know if that helps, but it`s about all it gives other than options for switched pumps which you can address when you get the unit working.I should have said the wires at the switch end fasten to screw terminals on the printed circuit board.