3 flipping hours to wire up 2 switches - would you believe it!
Still, here's the result. The extinguisher power pack is above the glove box and the internal switch is on the lower dashboard bottom right of the "E" sticker.
It was quite a relief when we tested the circuit and the correct green light came up.
Now it's "just" a question of the plumbing - the pipework and nozzles. Next week's thrilling installment!