On the alternator side, I did see one diagram for an MX5 that suggested:
grey to alternator light
grey/red to switch 12v supply
white to main fuse block (and presumably then to battery)
This is the image, but it's from an image search and without the accompanying text it may well be no help. It's clearly trying to by-pass some sort of control unit:
This other image is suggesting a diode in the circuit, though this has different wire colours so may have other differences.