Tim, you don't happen t have a single contact bulb in the RH tail light, do you.  That would short the brake/turn wiring to the tail light wiring.

John - "The Hoosier Hurricane"

Or U may have a double filament Bulb with one Filament burnt out. I would replace all 4 Bulbs in Parking and Tail Lights with new known good Ones. See if that changes anything.

  

Tim, I wasn’t sure what year vehicle you’re working on, but I may have missed it. I’ve attached a wiring diagram for a 59 car which I used when I was having a number of issues with taillights, brake lights and turn signals on my 59 F100. Hopefully it will help you to know which wires go where.
Looking at the diagram you’ve supplied, the colors seem to match up with the 59 wires, so Ford probably stayed consistent. For example, you said disconnecting the blue-orange wire caused only the front right turn signal to work. Blue-orange runs right rear turn signal/brake.
I won’t go into all of the unexplainable things I ran into over two weeks chasing the electrical issues. I did have a ground issue, a light bulb socket that wouldn’t light up because of worn-out contacts even though power was going to the socket, and lastly, a loose connection that kept the right taillight from illuminating. I don’t know if the car has a flasher, but that was keeping the turn signals from consistently working. All is good now. Let me know if you want any specifics.

Soffian Adam
Jamestown, NY
59 F100, 55 Club sedan

I'll check that fuse today.

Light bulbs are LED and we switched 'em, right to left.

Sorry, should have mentioned that it is a '56 Crown Victoria

Tim try the System with standard Bulbs instead of LED Bulbs. Get it working properly before using the LED. Are U using LED Bulbs in the Dash or just the Front Parking  and Rear Taillights? I suspect part of your Problems are the LED.

  

LED bulbs are only in the tail lights.
I'll test your theory of using original bulbs and let you know what happened.
Thanks for the advice.
Tim

As I understand it the LED Bulbs are Polarity Sensitive. Not sure how that works with double Element Bulbs but getting it working with regular Bulbs eliminates that Possibility.

  

Took your advise and pulled out the LED's from the tail lights.
For some unknown reason, I looked inside the bulb housing on the right hand light.
BOOM/BANG !!! THERE WAS THE PROBLEM !!!!
In the housing, the green wire had worked it's way out and was shorting out against the other wire.
Put the green wire back where it belongs and PRESTO CHANGEO NO MORE PROBLEM.
Want to thank everyone who responded to this problem, YOU GUYS ARE PRICELESS !!!
Tim
Mud Key
Central Florida 33706