So I've altered the wiring to only operate the headlight with the ignition on.
I didn't come back and check what Adrian had said, and I've wired it from the positive side of the coil to position 3 on the light switch (removing the old brown wire from 3).
It operates as I want and I've done 150 k's so all seems fine.
Any issues with doing it like this?
Cheers, Geoff.