The trailer light fuse on a 2019 Freightliner Cascadia is typically located in the fuse box, which can be found in the engine compartment. Specifically, you should check:
: Many trailer light failures on this model are caused by faulty pigtail cords or corroded pins at the 7-way plug rather than internal truck issues. Freightliner Cascadia Trailer Light Fuse Location - Q&A 2019 freightliner cascadia trailer light fuse location
Located on the driver-side firewall under the hood. The trailer light fuse on a 2019 Freightliner
: If a circuit shorts, the SAM module stops sending power. Try cycling the ignition (key off, then back on) after unplugging the trailer to see if the circuit resets itself. 2019 freightliner cascadia trailer light fuse location