I had an issue like this after fixing the reflectors for the dash lights... I just scratched up the soldered contacts a bit (in case of any oxidization), added some contact (dielectric) grease to each individual connector, and reassembled the dash again (3rd or 4th time by then), and all the guages worked properly again.
If you haven't fixed the dash lights and/or odometer gear (assuming it's broken), now's a good time.
