Negative switched?????

Hi all, i am a little stuck, or confused about wiring spotties with negative switched headlights. I believe that i wire it as follows,

Relay pin 30: Battery power
87: Power to spotlights
85: Negative hi beam wire
86: Positive power from switch

Can someone please give me an idea to what size cable i should be using for pin 85, the earth wire from relay to headlight earth wire. Will be using 6mm twin core for the spotlights so thought the earth should be equivalent of positive wire. Surely i couldnt tap wire of that size into the headlight earth wiring? Can i just earth the relay on its own or does it have to go to the headlight earth wire.

More importantly though does anyone have a diagram or something of how this works as i cant work out how to wire up the switch. I dont get how you get power to the switch without having power there all the time like the headlights do. As i have a light on my switch i dont want it glowing all the time.

Pretty please help me out.
Cheers