74 Buick riviera

Greetings, is it when the engine is running or when the vehicle is in motion? If it's when the engine running, I would check the fuse with a test light, that controls the cluster/dash . My reason for suggesting using a test light is because sometimes, the fuse may show that it's good when in fact it's too weak to regulate the current needed. If it's the latter, I suspect the connector(s) behind the cluster needs to check, because during the vehicle motion the vibrations is causing the connectors to disengage. Good luck..SEMPER FI