How can i fix my vauxhall cavalier?

I have a vauxhall cavaler 2.5 v6 on a M plate. I am getting no charge from the altenator to the battery. I have replaced the alternator which has made no difference. On switching the ignition on there is no battery light on the dash, when the engine runs this light does glow but is very, very dim. I have checked that all the earth connections which are good. The battery is also in good condition.