I just fixed two gauge sets that had this problem. The solder joints on the gauge board where the connector comes in crack and fail. This causes the gauges to operate intermittently.
The gauge set needs to be pulled out and then the circuit board removed (just screws), flip the board over and re-solder the connector pins on the board. Put it all back together and all will be well. The only problem might be finding a geek (like me) to solder it for you.
Note- don't buy a used gauge set, they are likely to have (or soon will) have the same problem. My uncle had done that, which is why I ended up fixing two sets.