96 C280 CEL and Instrument Cluster Question

[Seaurchin]

Check Engine Light is on. OBD2 generic scanner gives code P0600 (Serial Comm LInk Fault). Any help where to begin? Which module SFI, DM, etc is not communicating on the CAN bus? Major (replace module) or Minor (resistance or ground problem)?

Just curious is it normal to have the LED panel lights stay on indefinately? The odometer/trip odemeter, clock, ambient temp LEDs stay on overnight? Any ideas what might be problem if this isn't normal? Ignition Switch checks out OK... TIA