A friend'* 93 SSE had a similair problem, except the symptom was that only the speedo and tach contiued working. Cleaning the contacts didn't work in that case either. The problem was poor solder connections. I re-soldered most of the connections on the boards, but I believe the problem was the soldered connection to the to the spring contacts that connect the boards together. Just be careful with the amount of heat you apply - you don't want to lift the circuit board traces. I used a 800 degree themperature controlled soldering pencil. A 30 watt pencil simliar to what you'd get at Radio Shack wasn't hot enough. It'* been working for about 9 months now.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.