If the dash frame and the car body have both been painted, it may be loosing the ground connection where the dash frame bolts to the door jamb by the drivers and passenger doors. I learned that lesson the hard way with my Superbird back in the 80's. Since then, I leave those areas of both the dash frame and under the bolt in the door jamb bare metal and coat them with dielectric grease before bolting them together. There should also be one screw on the cluster that grounds the cluster to the dash frame. Make sure your negative battery cable is on bare metal where it attaches to the body too. Steering column needs a good ground. Good luck with it.
