Tail Light Problem

Hi, I have a 1982 Toyota Pick-up and I am having problems with my tail lights. I know the problem is in the wiring harness from the box back to the lights because when I dissconnect the connection in the bab all the blinkers work fine.
I tested the connector and it shows that the red has a steady current (from fuse box?) and there is a yellow wire with a red line that has a blinking current.

Anybody know what might be the problem?

Thanks,
Chris Poirier