It should light up - You will need a replacement bulb from the main dealers - I couldnt find one anywhere else (including Halfords). Remove the Instrument cluster and just hlaf-twist in the replacement.
Getting the instrument clusterout is a bit fiddly, especially when you need to reach round the back to un-plug the speedo cable, but it is an easy job amd should take no more than 20 minutes to do the lot.