1154 bulb?� Does that match your driver's side bulb?� I'm familiar with 1157 (dual filament) tail/brake bulbs and 1156 (single filament).� Do you have custom taillights?
Have you verified the circuit to the socket is hot when power is applied via volt meter?� Have you tried swapping the driver's side bulb in to verify operation?
Okay interesting question I pulled an old 1154(6V) that frankly looked okay. My other tail light bulb also looks like a 1154 and works but I have not pulled it yet. Some corrosion is holding it pretty firmly in place. I have the original tail lights on the Jeep nothing custom. I have yet to do the volt meter.
Had the Jeep out quite a bit today teaching my 16 year old son how to drive bringing back quite a few memories of my Dad teaching me at 12 in this same Jeep. With 500 acres to roam that was a sure lot better than a bicycle during the summer. And the good news it seems to be settling down and overall running pretty darn good. Multiple start-ups today with no choke and right to idle.