How to fit a trailer board to a Multipla

Has anyone done this yet. I have purchased a trailer board and wiring kit from halfords but am unsure which wires on the lighting loom are for which
lights (indicators, fog, rear etc). There are 5 wires on the back of the rear lights panel but I have 6 wires to connect (expect 6th wire will be for the number plate).
Can anyone match up the wiring colours?
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