I have an auto dim mirror, i know if i connect to a + & - it will work, as i dont have the loom i plan on taking the live from cig lighter.
My question is where is the reverse switch and can i get to the wires without going all the way to the boot.
I plan on using the reverse switch to turn off dim on mirrror when reversing so am i right in saying i can connect the grey wire to the switched side which will be switched to earth.
Also have the down light which wires activate it i plan on connecting to switched interior light so it comes on with them.

I have the 4 wire auto as below.

1, Black, +12V
2, Brown, GND
3, Grey, Pulled up at 12V, Connect to ground to cancel auto dimming
4, White/Black, Pulled down to GND, Connect to 12V to cancel auto dimming