Three Reds
One is power coming in
One is power going out to the next ceiling rose
One is power going off to the switch
None of these Reds connects to the new light - they just join with one another - all three.
One Black is Neutral coming in
One Black is Neutral going off to the next rose
These two should join together
The THIRD BLACK is power coming back from the switch (Switched Live) that turns the light on and off. To properly identify it it should have a Red or Brown sleeve on it or sometimes a piece of tape and sometimes nothing at all which is very naughty.
The new lamp connects Neutral (Blue probably) to the two blacks and Live (Brown probably) to the single black - the Switched Live
Your challenge is to identify which of the three black wires is switched live...
http://www.flameport.com/electric/lighting_circuits/lighting_ceiling_rose_other_colours.cs4
Stay safe
Peccavi
October 2009