speedometer and tacometer work off and on as well as odometer whats the problem?

I have a '92 Cabriolet with the same problem. There is a tiny black 10 volt transformer circuit on the back of your cluster. It looks like a computer chip about the size of Chiclet gum. It's usually black in color and has three prongs and a screw to hold it in place. It's on the backside of your instrument cluster. You can test it with a voltage meter. If it's getting 10.5 volts or 9.5, it's bad. You can either order one from VW or pull one from an old cluster. Either way it's a major pain. A new cluster may be just as easy since you have to pull the whole dash apart. Or for like .75 cents you can order one through www.mouser.com. Part # Ka7810aetu