There should be 3 sections on the ceiling rose - 2 sections with 3 terminals and the other section with 2 terminals.
Switch off the power at the consumer unit!
Take one of the red wires out of it's terminal and wrap some electrical tape around it to make sure it can't touch anything.
Turn the power on and have a look at what comes on - ideally you want the second light not to come on at all.
Turn the power off again and try taking out a different wire until you get this.
When you have found the live wire which controls the other light put this in the section of the rose which has 2 compartments, and should already have 2 wires going into it - one coming from the switch (should be a black wire with a red sleeve on it) and the live going off to the first light, which is currently working.
Switch the power back on and everything should work properly (he says!)
Adam
January 2009