You do not mention a fuse or breaker blowing when you pulled the switch cord - had this been the case then you may have accidentally put one of the Black wires in the wrong place.
Three reds together is jut what you need They bring power in take power out and also take power to the switch.
Power returning from the switch will come back on a black wire - you have 3 black wires two of which are Neutral and one is Switched Live - confusing and potentially dangerous so the Switched Live should be identified with a red or Brown sleeve. It is this wire that should attach to the Brown that goes to the light fitting.
The Blue is the Neutral return from the Light fitting and connects to the two Balck Neutral wires - Neutral in and Neutral out.
If you're not popping fuses and all the other lights in the circuit are working properly your wiring arrangement is very probably OK and the pull switch must be suspect if the new fitting does not work.
If you are popping fuses then you've mixed up one of the Black wires.
The new fitting may of course also have a fault - a bench test with scrap cable into a wall socket will tell you if its good.
Take care... Good luck...
Peccavi
February 2009
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