I'm pretty sure that the taillights and the dash lights are on separate circuits.
They even have separate terminals on the HL switch.
Coming from nowhere----it might be a good idea to check the HL switch as this is the common starting point for both circuits.
Could be something in the switch has broken and fallen against the metal body and the buss inside the switch connecting the tail/dash lamps.
Check to see if you have 'park' lamps, I think they are on the same as the taillight circuit---------however, still a different terminal on the HL switch.