Wrong number of wires in my ceiling light?

[LdA]

I'm changing the light fitting in a room (with a single switch), and the way it seemed to have been wired was that one black wire went to the live in the lamp, and the other went to the neutral, while the two red wires were taped together.

Not only does this seem to be one red wire short, but I can't work out how it ever worked in the first place. Can anyone shed some light? (hahaha)

 

[GarethW]

Normal if it's the last one on the circuit,
one of the blacks should be sleeved in red tape.

 

[LdA]

OK - that makes sense. Sadly nothing is sleeved in anything. I hooked up the new lamp the way the old one was and it doesn't work.

So, I'm guessing I put the two reds in the loop blocks, but how do I work out which of the blacks go where? Or am I safe to just reverse what I've done and hope for the best?

 

[sparkwright]

The black that gets sleeved red that goes to the LIVE of the light goes to the light switch.

Can you trace this cable?

 

[LdA]

Not that I can work out. It just goes up into the ceiling with the others.

 

[EFLImpudence]

Not only does this seem to be one red wire short, but I can't work out how it ever worked in the first place. Can anyone shed some light? (hahaha)

http://www.diynot.com/wiki/electrics:lighting:lighting_circuit_layouts

 

[GarethW]

Do you have a multimeter ??

 

[LdA]

Oh - yes I do! Let me guess... check the wires with the switch on and off to work out which is which?

 

[GarethW]

Yep !!!
Just to be safe, turn off your main switch in your consumer unit.
Select the continuity test, put your probes together and it should read close to 0.00 ohms (probably 0.01 to 1.00 ohms).
Next pick a pair of red and black, put a probes on each one, flick the light switch, have you got close to what you had from above ?
If not try the same test on the other pair of red and black.
Once you have found the switch wire, you must tape the black with red or brown tape.
The other black that you are left with is your neutral and the red is the permanent live, the red and taped red or brown wire is your switch

 

[ban-all-sheds]

I hooked up the new lamp the way the old one was and it doesn't work.

If the second part of that statement is true then the first part is not.

So, I'm guessing

Please do not do wiring-by-guesswork. Properly identify the conductors by tracing and testing, and connect them on the basis of actual knowledge.