wire connecting

Hi All, I was think of wiring up a indicator buzzer just like I had on my 2Cv. The wiring is a different size on my K11 1998 model more like usb cable wiring, so when connecting exterial wiring to the car wiring which is better solder the wire to the green/yellow wire or a anything else.
also I have a cigarette lighter which is not coonected and have two black connections not atteched to anything directly behind siad unit, any idea what there for. Peter0003
 
Not just replace the relay with a noisey one? Like a bike one or something ,
And one will be for the lighter (it's looks like a L ) or which ever fits and second , depends on what it is plug wise
 
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