What does this wire do?

Hi first post, I'm in the process of putting a cg13 in my mini and I have it running. I'm using a nippon denso alternator off a daihatsu sirion..
With regards to the micra alternator wiring I've 2 wires. One big one which obviously goes on the threaded terminal.. And I have another wire with a smaller loop fitting. What is this wire? IGN? Live?

Thanks
 
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