The tail light is a separate circuit, separate filament in the 1157 bulb. Make sure the bulb is good.
It's also common in the factory tail lamp that the contacts get flattened out. Pushing rather hard in on the bulb may light it. If so, remove it and reshape the contacts. Inspect the solder contacts on the bulb itself to be sure they are both prominent enough to make good contact.
Finally, the tail light, instrument illumination, tag light and "city light" are all on a common circuit that bypasses all relays and runs through Fuse 6. Since your tag light is burning, I would suspect the contacts or bulb in the tail lamp itself. (You can look in the bottom of the headlamp to be sure the low-watt city lamp is burning).