trouble shooting opinions

[Ultrasummer]

Finally to the point where I can focus on trouble shoot some electrical gremlins. 1968 C10 stepside. 307 4 speed.

I'm getting ready to work on some electrical issues this weekend. Before I get to it, I thought I'd throw it out there and see if anyone had any opinions. Here's the problem. Turn signals don't work front or back. New tail lights only work on driver's side but not on passenger side. License plate light works fine. New rear wiring harness for new rear tail lights. No lights at all on passenger side rear.

I'm guessing a fuse might be the turn signal issue (that big silver guy in the corner of the fuse box). I can only figure it's a bad wire between fuse box and new rear wiring harness.