Hmmm, could be an Elky thing.

I have a '69 El Camino that I have restored, complete with a painless wiring kit, and my tail lights do not currently work. But the rear side markers do work as does the brake lights.

I am thinking that it must be a grounding issue or maybe my construction of the splices or

Good luck flanker, let me know if you come up with an answer and I will do the same!