Bad Ground on my 67 Valiant Dash Cluster?

I have a 67 Valiant. The temp and amp gauges worked well until one day I took the cluster out to replace the dash lights. While testing the lights, (I had the engine running,) the gauges were up and down totally erratic. I turned the engine off, and then turned the key "on". The gauges never moved again. Obviously, I shorted something out. I've gone over the circuit board with a test light and ohm meter. I changed the voltage limiter. No help. One strange thing is, when I check the positive and neg posts on the circuit board, I'm showing 12 volt on pos and neg. I don't think that's right. Could this be my problem? Please help.