Similar '97 Jetta GLS Electrical Problem?

[DeadVW]

Hi,
I love my "new" '97 Jetta GLS. BUT...
While driving, my tach, speedometer and aftermarket radio shut off. They come back on if a rap on the tach/speedometer window a couple times or if I "reboot" the car, but a couple of miles later they shut off again. Now the battery's not holding a charge, but that may be a different issue altogether--I'm not the expert; you guys are.
I was told that it may have a bad body control module but the dealership guy said that there's no such thing in this model. SO... what do you guys say?