Alternator trouble

Since I've had the car the alternator warning light has always been lit up to indicate the battery is not getting charged when the engine is running.

We took the unit off to have a look at the connectors today. It looks like all the connections are fine - this one has three poles within a single connection - so chances are the alternator is duff. Getting the unit off is pretty easy - there are just three bolts which didn't take much to loosen. The bottom bolt also acts as an adjuster to make the belt tight.