This manual is referenced in "Guide to DRB III" p27: (YES, I've seen the cursed RED LEDs)
Error messages come in several forms. The first is when the DRB III is unable to communicate with a given controller because of a Bus fault. In addition to the error message, the LEDs in the middle of the handle wil glow RED. In this case, before using the DRB III to read out DTCs, it will be necessary to restore Bus functions. Refer to the appropriate Vehcle Communications diagnostic manual for the vehicle you are servicing.
I can't find any such manual searching internet or on factoryrepairmanuals.com. I have seen VCD manuals for other models and years but nothing for 1996 or Viper.
I am beginning to suspect these are for OBDI?
I think I have the answer to this: "Guide to DRB III" was published in 1995, the last year before OBDII.
Evidently these "communication manuals" were OBDI.