How do i fix rev counter?

I have a similar problem with my 306. the rev clock is and has been dead sinse I got the car. it started working after I drove through a massive puddle and another car splashed water over my bonnet. tho only worked for a day or so. now I know it works, its just buggin me that its not working without driving through a river. lol. Help please

trucker glenn
January 2010