Start by running a test to the rear wiring harness connector using a different known-good 12+ source and verify that it's not your rear wiring harness. That will tell you if your harnes and lighting grounds are ok.
Use a test light to verify power at the source for the brake and tail lamps, if you haven't already.
I'll try and look at the rest of your harness diagram on-line, but if you post it, that would be helpful.
I have had a driver's tail light not work due to a partially melted turnsignal switch contact.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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