If memory services me right there several things on that circuit besides the tail light. Seems the tach and horn are also on it.
the horn is instead on the Stop fuse circuit along with the turnsignals. The Stop and the Tail Light filaments are in the same rear bulb but the circuits are designed separately to avoid a situation that you don't have any rear lights as would be the case if the Tail and Stop were on the same fuse and one caused an overload disabling both un-isolated from one another. The excess capacity on the Tail Light fuse is used by the meter electricity, instead of the meter having a separate fuse of its own, thusly, "Tail/Meter" fuse. I'm unclear on the idiot lights .... if only the neutral indicator is wired to the Tail/Meter fuse circuit and not the adjacent high-light indicator and the turn signal indicator since they're not interconnected. Whereas, the oil, sidestand, and water temperature lights in the tach housing are wired to their corresponding circuits, er, not to the Meter/Tail circuit. Despite those little lights being in the tachometer, they're not wired to the Meter fuse. Anyways, the Tail/Meter circuit doesn't have anything to do with the auxiliary lights unless it was mistakenly tapped into or incurred collateral damage from whatever. The auxiliary lights should have blown the headlight fuse, so something's odd. (as frequently the case)
