Did this happen after the cluster swap? Have you done a search on the forum for similar problems? It sounds like a big voltage drain with the brakes or signals on.
Crazy as it seems, make sure all your grounds are good.
I was hoping you could help me. I have a 94 caprice wagon. Out of the alternator the voltage is fine. But when I'm at a stop using the brake and or the turn signals the gauge starts moving into the red. I have changed the starter, battery and alternator.
Now, I have replaced the oh cluster with a 95 impala cluster. The machine seems to think that the new cluster may have an option that the original one did not have.