If you connect a lead to the 12v starter point at one end, push a sewing needle carefully into the Green/White wire on Pin 1 of the webasto and touch the wire to the needle the Webasto should fire up and keep going for as long as you keep that connection in place. Putting 12v on Pin 1 will (should) switch the unit on, which is how the DIY version works.
In normal operation the Webasto only comes on below 5C, and the Auxiliary Heating mode requires a good battery and sufficient fuel.
The unit is normally enabled as a coolant heater in the UK by default. Full auxiliary heating was enabled if you paid for the Telestart option at new, or had it retrofitted.