Lost brake and blinker

[Northwest Outlaw]

1961 Apache10.
Thought I had everything worked out, but nope. I'm posting this at 1am after wasting an entire evening chasing gremlins only to get right back to where I started, without passenger side brake light or blinker.

Tail lights work fine, both the same brightness.

Weird thing is both blinkers work when the taillights are off, but only driver's side works with the tail lights on. When the taillights are on and I try the passenger blinker, the license plate light pulses.

Any help much appreciated. Thanks