2002 TRD left Signal/brake light issue question.

Okay guys, I have another question about tail lights. 2002 TRD


Drivers side rear turn signal works fine until I apply the break, then goes crazy. It makes the break light blink and the turn light then goes out. Let off the break and it works fine.


I removed the old trailer harness thinking that was the issue, and it worked for a day, then started doing it again.


Connectors look okay, and thinking might be a ground problem, tried finding that and couldnt.


Could this be something to do with the truck signal controller?


Somebody please give me a place to start, and thanks in advance.