I recently bought a 1990 kw w900b. My turn signals and hazards work but my tail light don't. I've checked the fuse box but no out fuses. Could it be the low end of the bulb or the wiring on it?
If it has those rubber-mounted things inside, they are notoriously touchy about making contact with the bulb (in my experience). Check all the connections and bulbs. There might be an auxiliary fuse box in the dash, under the hood, or in the side box. Best I can offer.