Well, the taillights, parking lights, and lights for the instrument console are ALL on the same circuit. But I'm pretty sure that they AND the headlight circuit draw from the same large fuse in the engine compartment that goes into the headlight switch part of the combination switch.
So I think the issue is in that headlight switch - even though the headlights are still operating, that's a separate circuit. I know - because this happened to my '88 B2200 about two years ago.
Axel Breaker Earl has a nice write up to clean the contacts in the headlight switch, see
If you do buy a new or used headlight switch, be aware that there is a white 4-connector type and a black 5-connector type.
white 4-connector type, note 4 male terminals at top of photo
black 5-connector type