Wiring for 12vdc socket in load area

[John Bilko]

You could be right about the third wire, very good observation. I'll check the diagrams if I can find that daft socket in them, to confirm.

Normally nothing can be left on, as Eco mode takes over and nearly everything is powered from the BSI itself.

I have learned one method to keep Eco mode from coming on, but use at your own risk (your battery can be flattened and the BSI risks corruption from that) - the answer is to leave the hazards on while using the internal electrical items (no engine running), then the Eco system will never interrupt otherwise it would cut the hazards off, and it is designed not to do that. It seem that the BSI waits until the hazards are no longer on, before cutting in with Eco mode.

That is BRILLIANT.  I'd add a thumbs up if there was one.
I am going to use that suggestion - I will keep an eye on my volt meter.