I ran 12V directly from the battery to the rear wiring harness and the brakelights work. So I would think I've eliminated the rear harness as the issue.
But - what would be different about running 12V directly from the battery, vs. 12V from the brake pedal switch? (Which is were I was tapping in for 12V to test the harness).
Voltage from the battery was 12V, voltage from the brake pedal switch was about 11.5V. I can't see that making a difference.
