Front parking light/turn signal stays on

In my case it turned out to be a short in the trailer, right on the back side of where you plug in the light cord.

 

Did you check the flasher? Some trucks I have driven had 2, one for each side. I have never driven a Cascadia, so I don't know if they use 1 or 2. Or even where the fusebox is to check.

 

It could that the Turn Signal Stalk is bad.

 

It could be hard wired...I have had a Pete and a KW that have odd turn signal quirks. The inside would blink fast on one side and slow on the other (like a bulb was out) but all the lights outside were working fine, and flashing at a different rhythm than the dash. Technology, making our lives so much simpler...

 

The Cascadia does not have a flasher, the Sam_Cab module controls the trucks signal lights directly. The trailer lights are controlled through relays.

 

Yes, that is a possibility. Does it do it with or without a trailer?
Mine did it with the trailer attached, but I pull two trailers, so I had to try them both to isolate it to the front one.
Then I disconnected various lights, until I had them all out, and the light still stayed on. Then I knew it was a wire issue.
When I pulled the light cord socket out of the front of the trailer I found many of the set screws for the seven wires were loose. One actually fell out and was shorting the right turn and clearance lines together.