Reverse light cable colours ?

I'm going to fit a "reversing parking sensor" to my Ford Cougar (closest possible to Focus). The device has two wires which need to be connected via
a clip to the two wires (+ and -) that connect to the reverse light.
Without me having to take off the rear light assembly, can anyone tell me what colours the + and - for the reversing lights are, or do I have to make sure which pair of leads goes to the reversing light( if the colours are the same for the breaklights/rearlights etc).


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