MegaSack DRAW - This year's winner is user - rgwb
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How on earth do you wire an LED with two unmarked white wires to a 3core lighting loop cable?
Carefully
You use a junction box. Obviously you need to identify the incoming wiring (lazy electricians like to use pendant fittings because they only need two core cable) but the LED won't care about live / neutral.
Ah ok, I'll try my best to keep brown and blue apart then!
But blue could also be live... you also don't make clear whether your cable is three core and earth, or two core and earth (but three wires). You would usually use three core between two-way switches, not to the light fittings themselves
You need to figure out whether you have a permanent live at the fitting (old way) or whether it runs to the switch first (sensible way).