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I agree with above as a possible cause. Could also be cracked conductor on the Circuit Board (happened on mine, was able to Spot it and Solder fixed it.)
Lots of other potential failures/intermittants. Eventually, I had to send mine out for refurbishing. Over time, heat/cold cycling and vibration takes its tole.
I have the Factory Service Manual (85 Corvette) and bought a copy of Gordon Killebrew's "'84-'89" Corvette Digital Cluster" Manual. Still, mine eventually needed that refresh.