I know this is a really old thread but hopefully someone can clarify.
Im chasing an issue in the wire that comes from the inertia switch / telltale.
Is that wire a 12v supply?
on the wiring diagram its from the central ac switch.

In the diagram above there are 2 wires going to each lock/unlock switch.
In reality there are 3 wires. Or is the 3rd earth? Can someone explain what
each of the 3 wires do on the switches please?