Renault Trafic 1.9 DCI 2004 electrical problem?

I have a slight problem with my Renault trafic!! I think it's an electrical issue as the van starts fine but once running the glow plug light fickers on and off and the rev counter flicks about on a steady constant throttle!! I have had the alternator checked and it appears fine also I have check for water in the fuel filter as the manual says the light also indicates water in the fuel. Anybody have any answers or had the same problem. Cheers