Urgent Help Pleeeeeease

[bronkone7]

Hi All
Have had problem with car not starting since Friday.
Was told needed new battery.
Now putting battery back have come across brown & black single wire coming from loom at which end is 4 black & white wires.
Don't remember taking this off but it only seems to reach around the battery area.
Have put volt meter on it and got 8 volts showing.
Could someone look under there bonnet please.
Megane 1600cc 53.
Thanks
Brian