I took out a light fixture in a bathroom with the intent of installing a new one before and I came across 4 sets of wires. This bathroom light (I think) is connected to an extractor fan and is on the middle floor of a three floor house and connected to a three-switch box that controls the bathroom, middle corridor and downstairs corridor lights. The original setup of the light fixture is in the photos that I have attached below. Within these the wires are:

  • Green/Yellow, Brown, Blue
  • Green/Yellow, Brown, Blue (with black electric tape tag)
  • Green/Yellow, Brown, Blue (with brown electric tape tag)
  • Green/Yellow, Black (with brown electric tape tag), Grey

How they were connected to the original bulb is pictured below.

Picture of Fixture before taking apart

enter image description here

I have attempted to connect these cables up in the following way: (with purple denoting the brown tag)enter image description here

However, lights downstairs and lights on the middle floor keeps tripping the entire house sockets and lights breaker. How can I go about effectively fixing this? Thank you

Based in UK

  • You may want to add which country you're in, that could help identify the colours. The wires look German or Dutch, in which case you should never connect black to blue. Blue is neutral, black is switched hot.
    – Paul
    Commented Mar 9, 2023 at 12:39
  • Also, what was the grey wire originally connected to? I don't see any grey in the pictures.
    – Paul
    Commented Mar 9, 2023 at 12:40
  • @Paul Thank you for letting me know, I am based in the UK! The wire you can see really faint beneath other wires by the connector in the middle of the first picture! I’m not sure what it was connected to before as when I started to pull everything apart the wires starting falling out of connectors Commented Mar 9, 2023 at 12:53
  • Good on you for taking before pics! So few think of doing that - you'll be a great Home Made Electrician! ;) Hang on... someone will be by shortly to help you out.
    – FreeMan
    Commented Mar 9, 2023 at 13:18
  • 1
    In your 2nd pic I see blue-with-brown-tape and black-with-brown-tape connected together, and to the brown-to-the-light-socket. But that's not what's shown in your diagram. I also think I see blue-to-the-light-socket connected to two other blues, but nothing like that in your diagram.
    – brhans
    Commented Mar 9, 2023 at 18:09

1 Answer 1


This is quite a the sticky wicket. So to be clear, there are four cables entering the light fixture, all with three wires contained in the cables. All four cables have green/yellow wires, three cables have brown and blue wires, and the last cable has a black and a grey wire.
Most likely, the black and grey cable is your line voltage. I would take all of the connectors apart and take a reading on the black and grey to confirm. If you get no reading, try flicking on and off the light switch. If you have also switches at the bottom and top corridors to turn on and off the corridor lights, then it's quite likely that two of the other cables are the "traveler" cables for the two three way switches. The final cable would most likely go to the fan, and be connected to the red and blue wires which I understand to be your light fixture.

  • 1
    Assuming that the wiring was up to current code (for the UK), brown should be line voltage. Black used to be line voltage, but then there should have been a red wire in there...
    – Paul
    Commented Mar 9, 2023 at 17:20

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