4 wires into 3

[Orlasdad]

I offered to install an outside light for my sister. The cabling from the house was already in situ and terminated in a plastic junction box and had not been used for years. I removed the cabling from the box and discovered 4 wires, I green/yellow, I red, I black, and 1 blue. The light only had, green/ yellow, brown and blue. I connected both green/ yellows together, the red and brown together, and the blue and blue together. I isolated the black. I hit the switch in the kitchen, the bulb flashed ( not flickered) and continued to flash at random. I disconnected everything, brought the new light home, connected it to a 13 amp plug, and it worked beautifully. What am I doing wrong?

 

[pete01]

You've probably got permanent live switched live, neutral and earth.

You'll need to test to find out what's what.

I doubt its 3 phase as suggested above.

 

[opps]

I think you need to go back and test it with a multimeter to find out which is (edit-typo) perm live and which is the switched live. As above, I have never heard of a 3 phase light fitting at a domestic property.

 

[Orlasdad]

I tested the red wire and it was live

 

[pete01]

What did you test the red to?

 

[Orlasdad]

A gadget that I have. It bleeps when it touches the insulation of a live wire

 

[pete01]

The black you isolated is probably neutral, not the blue check the wiring inside the switch.

 

[RandomGrinch]

Are there any other external lights or PIRs installed?
Four wires can be used for a PIR sensor to send a signal to illuminate many lights.
It may be possible that you used the signal wire instead of the live, or the existing connections are corroded through disuse?

 

[bernardgreen]

The 4 wires might be to enable a PIR ( Passive Infra Red ) sensor to control the lamp as well as an override function by a switch inside the house,

Colours may be dfferent to those in the diagram