Chrysler Repair: 1989 new yorker odometer and fuel gauge, side kick panel, hasty conclusions

Question
my dad has a 1989 New Yourker Landau. Its odometer is blank with a *. I did the ck by holding the 2 buttons on the dash and recieved a code of 999 and 921. I understand 999 means the cluster is good. But I don't know what 921 means and why the fuel gauge reads empty all the time when the tank is full. Also he has been experiancing a dead battery from time to time and the battery is good after its charged up.  

Answer
The 921 code code means there is a lack of messages being received from the body control module.  The diagnostics are bried and say right off the bat to replace the BCM though I don't like jumping to such hasty conclusions without much testing.

I believe the BCM is located in the right side kick panel and is subject to getting water in the connectors or the BCM itself.  It's possible that a new BCM will fix the problem but my experience with pre-obdII electronics is limited.  If you need wiring information let me know and I will see what I can find for you.
Doug