Thank you TTC for your fast response.
I tried to make a note whilst the fan was in situ and I also took a photograph. Even with these I am not absolutley clear.
However the old fan had a terminal block with five connections and looking at it from left to right I see the following:
Connection...
The pull switch in my shower room operates the light and the extractor fan.
The fan has packed up and I have bought a replacement; Vent Axia Silhouette 100T.
The problem is with the wiring. The old fan connections consisted of 2 Red wires,1 black,1 blue 1 yellow and the earth.
The new fan...